A threatening letter forced the evacuation of a Nassau County government building Monday in Mineola, according to authorities.

Sources tell News 12 that the letter was mailed to the Board of Elections, located inside the 240 Old Country Road building, and included the word "anthrax" and biblical verses.

The building houses several county departments, including the Board of Elections, the Department of Assessment and the county clerk's office. The fifth floor was evacuated as the Nassau police Emergency Service Unit assessed the scene.

Nassau County Executive Laura Curran says she's "thankful" for the rapid response.

By mid-afternoon on the fifth floor, most Board of Elections staffers had left for the day. It was a similar situation at the Assessment Review Commission, where people who entered the building to grieve their property taxes were greeted with a note informing them that work was being done downstairs.

The fifth floor was evacuated, but not the entire building. People could be seen coming and going from other offices, even as the Emergency Service Unit entered the building.

One person who works inside told News 12 that while his floor was not evacuated, many of his co-workers left anyway, not willing to take any chances.

Police say the building was deemed safe sometime between 4 and 4:30 p.m.