"is it ok?" - This is more direct, it almost assumes that the other person will say "Yes." e.g.
A: "Is it OK if I borrow your bike?"
"Would it be OK?" - This is in the conditional and is therefore less direct; it is more as a tentative enquiry, you're allowing the other person to say "Yes." or "No." e.g.
A: "Would it be OK if I borrow your bike?"
B: "I'm sorry, but I will be using it this afternoon."