Around 1:45 PM, police received a call from Del Mar High School about a student who brandished a gun and threatened another student the day before, according to the San Jose Police Department.
Officers arrived and placed the school on lock down.
Police said a weapon was not found.
The lockdown was lifted around 3:30 p.m.
Police said a 16-year-old female student was taken into custody.
An investigation is ongoing.