The Express-Times reports the lockdown happened at Nazareth Area Middle School on Wednesday morning.
The district says in an email that school officials checked the lockers of all eighth-grade students and scanned all the boys with metal detectors, but nothing suspicious was found.
The lockdown was lifted by 11:30 a.m. Upper Nazareth Township police say no one was in danger at the school.
School officials are reviewing video to determine who used the bathroom prior to the bullet's discovery.
Information from: The (Easton, Pa.) Express-Times