Yes — plain air-popped popcorn, with no salt, butter, or oil, is a safe and fun treat. Movie-theater or microwave popcorn is not.
Popcorn is just corn, and corn is parrot-safe. The problem is what we put on it: salt and butter turn a harmless puff into a sodium-and-fat bomb. Unpopped kernels are also hard enough to be a beak-cracking hazard for small species.