Galt Collegiate Institute in Cambridge was briefly placed under a hold and secure on Thursday morning, according to the Waterloo Region District School Board.
On Twitter, the board announced the hold and secure at 11:12 a.m. but 15 minutes later, the board announced that it had been lifted.
A spokesperson for the Waterloo Regional Police told Global News that officers are conducting an investigation in the area.
They said more information will be provided in the future.
This story will be updated as more details become available.