The blaze erupted around 2:30pm at Montgomery High School in the 22000 block of Old Highway 105.
Montgomery ISD Superintendent Beau Rees says a clothes dryer caught fire in the athletic locker room, creating a lot of smoke and triggering the fire alarms.
Students had already been dismissed for the day, and everyone who was inside the school was evacuated.
No one was injured in the fire.
Rees says the fire didn't appear to cause significant damage but they're still surveying the building.
Take ABC13 with you!
Download our free apps for iPhone, iPad and Android devices