Does your AR have a flattop, or a carry handle?
If it has a flattop reciever, it's no problem at all. Just pick up a set of rings that fit the rail on top of the reciever. Mine came with a one peice scope mount/rings that mounted right on top.
If it has a carry handle, things get a little more complicated. Most mounts that I am familiar with don't mount to the carry handle just real solid. Plus, mounting a scope above the carry handle will put your scope way up there. Might be a little uncomfortable. There are cheek pieces that mount to the buttstock that will raise your eye up on the same plane as the scope, and allow you to keep a firm cheek weld.