Los Angeles County sheriff's officials said Santa Clarita Valley deputies searched the campus after receiving a call about a person with a gun.
The school urged everyone to shelter in place as the search went on. It later announced all classes at the Valencia Campus are canceled for the rest of the night.
Approximately 200 staff and 2,000 students were affected by the lockdown.
Sheriff's officials said nothing suspicious was found.
The Canyon Country Campus classes continued as scheduled.