Need some more information. Are both pedals stuck? When did they seize up? Was the parking brake set when they locked? Peddle feel strange anytime before it seized?
Could be the parking brake. That's easy to check. It's possible the pedal is stuck on it's shaft. Undo the linkage and make sure the pedal is moving freely to check that. It's also possible something internal in the mechanism is broken or is binding. If all signs point here there isn't much to do but open it up and inspect.