An anonymous social media post prompted officials at Omaha's Creighton Prep to issue a lockout order Monday afternoon.
The matter was resolved without incident, school officials said.
During the lockout, students and teachers continued their normal activities, but no one was allowed to enter or exit the building.
The lockout ended after law enforcement conducted an investigation and determined that there was no safety concern.
Parents at Prep, which is at 72nd Street and Western Avenue, are notified of school safety issues through an emergency notification service.