Firefighters have extinguished a fire from an electrical switchboard at the Belconnen High School, Murranji Street, Hawker.
ACT Fire & Rescue has evacuated approximately 450 staff and students as a precaution.
Crews are currently clearing smoke from the area and conducting ventilation operations before allowing staff and students to return to the area.
Three fire pumpers are on scene along with the Hazardous Materials Unit, the Breathing Apparatus Van and one Commander.
Damage is minimal and there are no injuries.