Can I get a MA in Comparative Literature with a BA in Political Science?

Not unless you took a lot of relevant undergraduate classes despite having majored in Poli Sci.

Comp Lit is heavy on literary theory and criticism. You'd need some background in those areas, though extensive study of History or Art History would do. You'd also need to be able to read, at least, a couple of foreign languages to a university standard and to have some familiarity with their literatures. A lot of English classes would help, but Comp Lit is not just about English literature.

If you can truthfully say that you have that sort of academic background, go ahead and apply.

depends on the school you're applying to

http://complit.dartmouth.edu/graduate/how-apply

do you have those admission requirements ?