An envelope filled with white powder was received at a San Francisco police station Saturday morning, following five other such incidents Friday at Bay Area police departments and one Monday in Fremont.

The Northern Police Station on Fillmore Street was evacuated about 11 a.m. while the substance was evaluated. The station was decontaminated and the exposed personnel were cleared after the powder was determined to be nontoxic.

On Friday, police departments in Oakland, Hayward, Berkeley, San Leandro and Union City also received letters with mysterious substances, all of which were determined to be harmless.