They say the alarm was set off by mistake.
According to police, officers arrived on scene just after 11:20 a.m. to the 300 block of Avenue H at the Harvey Milk Memorial Administration building.
"At this time we have not confirmed an active shooter incident or located any victims," a police spokesman told ABC7.
SFPD says someone in the building triggered the alarm to report an active shooter.
But after officers searched room by room, they determined there was no threat in the building or anywhere on Treasure Island.
Police were conducting an unrelated active shooter drill in the city's Sunset District, which caused confusion, officials said.