According to the Bible, the word "antichrist" refers to one who opposes God, and who rejects the Message of Salvation through faith in Jesus Christ, God's Son. This description aptly fits the "son of perdition", who the Apostle Paul mentions in the verses below:
"Let no man deceive you by any means: for that day, [Christ's Return], shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition; Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God."
2 Thessalonians 2:3-4, KJV
Following are some additional verses regarding the antichrist nature:
"Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son."
1 John 2:22, KJV
"And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world."
1 John 4:3, KJV
"For many deceivers are entered into the world, who confess not that Jesus Christ is come in the flesh. This is a deceiver and an antichrist."
2 John 1:7, KJV
For more on this topic, please consider reading such articles as Who Hindered the Antichrist?
and The Kings of the North and the South