Why is the second beast of Revelation called the Antichrist?

An antichrist is "anyone or anything that counterfeits the true gospel plan of salvation and that openly or secretly opposes Christ." (See http://www.lds.org/scriptures/gs/antichrist?lang=eng) There are many antichrists today and they are everywhere. There will be many more who will have power to deceive those who are not firmly rooted in Christ. Lucifer is the great Antichrist but he has many followers, both spirit and mortal beings.

We learn from (1 John 4:3-6) that anyone who teaches that Jesus Christ was not the Son of God, but just a good man who had good philosophies is an Antichrist.

Personally I have always thought of the passage found in revelations (Revelations 13:11-18) to be referring not to one particular being, but of the idea, the attitude, the philosophies that will accompany those who are Antichrists. If you think of this beast not as a man or a being but more of an idea like money, power, scientific knowledge, etc. you can get a clearer image of the beast.

Revelation chapter 13 verses 11 through 18 describe the Antichrist, and his actions during the buildup to Armageddon, and even though the Bible does not implicitly call him the antichrist, many denominations, and many Christians have dubbed that individual as the Antichrist because his actions are diametrically opposite of what Christ did.

Rev 13:11 through 18 KJV

18 And I beheld another beast coming up out of the earth; and he had two horns like a lamb, and he spake as a dragon.

12 And he exerciseth all the power of the first beast before him, and causeth the earth and them which dwell therein to worship the first beast, whose deadly wound was healed.

13 And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,

14 And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.

15 And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.

16 And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads:

17 And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name.

13:18 Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six.

Just to add an answer to Cecil's, which is solid, but to elaborate more closely on the ideal of a personal antichrist.

Anti in the context of Christ refers to not only being opposite or opposed to, but also "in place of." Since, from Revelation, we see that this antichrist is given power and authority by the dragon (universally recognized as Satan), the antichrist is indeed a singular person -- but beyond that, he is meant to REPLACE the real true Christ, Jesus.

Just look at some parallels, again from Rev 13 as Cecil used:

3 And I saw one of his heads as if it had been mortally wounded, and his deadly wound was healed. And all the world marveled and followed the beast. 4 So they worshiped the dragon who gave authority to the beast; and they worshiped the beast, saying, “Who is like the beast? Who is able to make war with him?”

Two things here -- first we see the "beast" (the one empowered by the dragon, satan, has been mortally wounded but was healed). As a result this causes people to marvel and worship satan. This is a simulation of Jesus Christ's resurrection from the Cross.

The one goal of this is satan is prideful and wants to be in the place of God. Naturally his antichrist would stand to be in place of Jesus. We see this beginning in the Old Testament, for example, Isaiah 14:

12 “How you are fallen from heaven, O Lucifer,[b] son of the morning! How you are cut down to the ground, You who weakened the nations! 13 For you have said in your heart: ‘I will ascend into heaven, I will exalt my throne above the stars of God; I will also sit on the mount of the congregation On the farthest sides of the north; 14 I will ascend above the heights of the clouds, I will be like the Most High.’

Let's go back to Christ in the wilderness where satan tries to tempt Jesus. From Matthew 4:

8 Again, the devil took Him up on an exceedingly high mountain, and showed Him all the kingdoms of the world and their glory. 9 And he said to Him, “All these things I will give You if You will fall down and worship me.”

Satan wants worship, that's his only price for all the nations of the world. This is what got him thrown down from heaven, to the earth, where he has power and authority over this world until Christ's return; and this is his motivation for an antichrist. Christ warns us in Matthew 24 to be weary of false Christs and false prophets whom perform wonders. The dragon, the beast he raises up (the antichrist) and the antichrist's prophet itself imitates the Holy Trinity.

Again, to imitate, and be in place of, the true Godhead. Since Jesus Christ is our personal Lord and Savior, it only makes sense the knock off attempt to take his place for non-believers would be a personal savior-like figure as well.