The Lethbridge Police Service said officers will be present at Chinook High School during the school day on Friday after a threat was discovered.
Sometime on Thursday, staff found the threat written on school property and called police.
Lethbridge police said the investigation is ongoing to determine the veracity of the threat, but there is no evidence to suggest an immediate risk.
Classes will proceed as usual Friday and police said the increased officer presence is a precautionary measure.
The Lethbridge School Division posted a notice that school would proceed as normal on Friday.
“Anytime threats of this nature are reported, school and division staff work closely with Lethbridge Police Services to investigate the report and determine how best to proceed,” the statement on the high school’s website said.
“School will proceed as normal tomorrow and Chinook will have an increased police presence through the day.”
No further information was released and police said it would not comment further.