The threat came via a telephone call warning that one of three letter bombs would explode there during the day.
The offices were evacuated and, at first, police cordoned off a large area, according to Stockholm County's police communication center.
City buses were forced to navigate new routes around the area.
A pre-school and another school in the area were also evacuated, Christina Johansson, from Stockholm County's police communication center, told news agency TT.
Just after 10.30 am, authorities opened up part of the cordoned off area, but the building remains evacuated unitl 11.00 am when the area was declared safe.