Kitchener-Waterloo Collegiate Institute was placed under a brief hold and secure on Tuesday afternoon.
It was due to a weapons call.
Regional police said officers were called to the school around 2 p.m. for a report that a male had a firearm.
Police said they found the male in question on scene, but no firearm was found.
Nobody was hurt.
The hold and secure has been lifted and there is no threat to public safety.