Students at Canberra Grammar School were placed into lockdown for a period on Monday after a threatening email was sent to the school.
Parents were told shortly before 12.30pm that the lockdown was over.
Earlier, a lockdown alert was sent out to more than 2000 students and staff at the Red Hill school just before 11am.
An ACT police spokesman told The Canberra Times the school enacted its lockdown procedure as a precaution while officers carried out a search of the campus.
Parents have been notified of the lockdown via a text message sent by the school.
Parents were told in the text message not to attend the school and further information would be provided.
More to come.