CUPERTINO (CBS SF) – Streets surrounding Cupertino High School were closed and the campus was locked down due to police activity Thursday afternoon.

In a message to parents, the Fremont Union High School District said the school was locked down before 3 p.m. due to the activity in the surrounding neighborhood. A district spokesperson told KPIX 5 that the police activity was related to a call of "shots fired" off campus on a nearby street.

The Santa Clara County Sheriff's Office said an investigation determined that the noise turned out to be the sound of a vehicle engine backfiring and that no crime was committed.

As of about 4:10 p.m., deputies cleared the school and surrounding area. There is no threat to public safety and no injuries were reported.

Deputies said a reunification area for parents and students has been set up at the back of the school.