The LAPD was called immediately to investigate the device, and a bomb squad robot was deployed in front of the school auditorium.
An automated phone system was activated to urge parents, guardians and school staff to report to school as normal. Everyone was moved to a "shelter" location near the football field.
School officials said graduation, scheduled to begin at 6 p.m. will go on as planned with additional security provided.
No further information is available at this time.