The Gnostics were around during this time. That is why John said if somebody does not believe that Jesus came in the flesh, this is the spirit of antichrist.
1 John 4
2 By this you know the Spirit of God: every spirit who confesses that Jesus Christ has come in the flesh is of God,
3 and every spirit who doesn`t confess that Jesus Christ has come in the flesh is not of God, and this is the spirit of the antichrist, of whom you have heard that it comes. Now it is in the world already.
This is what my study bible says anyway.