Just plain air-popped popcorn is extremely healthy. It's just corn. BUT, the popcorn you get at the movies is covered in oil, and salt, and fake butter-flavored chemicals, and is extremely unhealthy. If you don't want air-popped, then Orville Reddenbacher makes some single-serving size bags of micorwave popcorn that have only 100 calories per bag. That's a pretty healthy snack.
It is if you make it homemade without the extra stuff they put on it.That stuff is really bad for you. Corn in general doesn't breakdown that good in your body, and turns to sugar fast, but I don't think it's bad for you :)
Make organic popcorn homemade with coconut oil and put nutritional yeast on it (it tastes cheesy) it's soo yum and is good for you!
As long as you air pop it, I don't recommend you buy microwave popcorn though, the artificial butter contains diaceytl and when inhaled it's toxic, also the bags contain a chemical PFOA and said it's cancer causing.