A 'hold and secure' put in place at Mother Teresa Catholic Secondary School on Friday morning was lifted after about two hours.
London police had placed the school at 1065 Sunningdale Road under the 'hold and secure' for what they called an ongoing investigation.
Police say a social media message about a potential threat spurred the police investigation at the school.
But officials said they quickly determined there was no threat to public safety.
Police confirmed that it was not a lockdown, and students allowed to enter but not leave the school. The 'hold and secure' was lifted at around 12:20 p.m.
The public is reminded to contact police directly if they believe there is a threat, rather than sharing it online.
