Yea, how have you been playing? Have you been check/raising alot of flops, betting low, then folding to a re-raise, and what reads do you have on your table. Normally, if i flop the nut flush, and i know theres players in the hand that like to bet alot of flops, ill check call or check raise, depending on the bet. With the check call, if a blank comes on 4th, ill check again, and when he/she raises, i push, if a card comes that could make a smaller hand, i may put out a small bet ( probably equal to the first bet of the last round) and hope for a re-raise, so i can push, and either double, of send the person on their merry way.
So many factors in this kind of decision, and not enough information in yer OP. Okay, you've got a HIGH flush; is it the nut flush? What is the texture of the flop? Action cards, junk? Us somebody else in the hand likely to make 2 pair from the flopped board? Are there straight/therefore straight flush possibilities out there? These are all critical to answer your question, and lacking from your description.