Could be anything from a piece of debris to incorrect hand size, poorly cut ratchets, a bent ejector rod, loose ejector rod, BC gap being way too tight, etc. Could also be a ill fitted trigger/hammer engagement or a broken part. Without looking at it or at least feeling it - I am just guessing here. If you have no clues, I'd seek a qualified Gunsmith - if there are any in your area.
Is this a recent purchase or have you had it for a while. If you have owned it a while, has this ever happened before? Has any work been done to the revolver? Any parts replaced?
ADDED: Probably not a real big deal, but if you are not familiar with the lock work of the gun, don't have experience working on them, I'd suggest not trying to fix it and let a Pro do it.