If you have either the 5.1.1 or 5.0.1 SHSH blobs, then yes you can. There's a sticky actually by f4780y about downgrading using SHSH blobs.
TUTORIAL - Downgrade iPad1 to 5.0.1 using SHSH Blobs and redsn0wFollow the instructions and replace 5.1 with your current 6.0 and 5.0.1 with 5.1.1/5.0.1. Once you're done and rejailbroken, go and get "No Update" from Cydia to block any future iOS changes unless you want to upgrade to it by choice.