It's not like an anti-Mormon, an anti-American, or "hostile towards" anything in that sense.
Anti, in the Greek, I just learned, can also mean "opposite, counterpart".
And that definition of the prefix, according to this article, is what Luther had in mind when he declared the Pope to be the "anti-Christ".
The church Michelle Bachman was a part of, the Wisconsin Evangelical Lutheran Synod, holds this stance too.
Now, I'm probably more surprised at this definition because it's been over a year since I've cared to read what the Bible said about the anti-Christ (somewhere in... Thessalonians?).
Still, having lived in the Bible Belt where Obama usually upholds this title, I always thought it was something more menacing. Maybe it still is under that definition. I don't know.
It'd be interesting to hear the full history of that term though.