Anti-Christ is anti (against, opposed to) Christ, which would also mean opposite Jesus. Jesus is good, anti-Christ is evil.
However, he has a trait which causes people to not recognize him. He "appears" to be good.
And the fact that he fools so many people is what gives him so much ground in a relatively short period of time.
He is full of deceit and he fools people until the time that he is revealed.
Catchy name, considering the subject and his position on it.