Police search and secured the headquarters of Facebook Inc. on March 11 after receiving a threat against the social media company.
The department said the threat against the Menlo Park campus turned out to be unsubstantiated and "totally not credible," according to Reuters.
The threat was reported a little after 7 p.m.
Facebook has declined to comment on the incident so far, according to the Associated Press.
Employees were held by Facebook personnel at the campus until officers reached the scene, Menlo Park Police Department spokesman Dave Bertini said.
Officers let Facebook employees leave at approximately 8:30 p.m.
"It was a totally not credible, unsubstantiated threat," Bertini said. "I am not even sure that it was specifically to the Menlo Park campus of Facebook."
Bertini declined specifically what the threat was, according to Reuters.
The San Francisco Police Department has not commented about the incident yet.
Over 6,000 people work at Facebook's headquarters, according to AP.