CGU Insurance employees were evacuated on Monday afternoon after staff members reported smelling gas.
Police and Country Fire Authority crews attended the incident in Myers Street, Bendigo, shortly after noon.
CFA senior station officer Darren Eenjes said it was a false alarm.
“There was a smell that came in from the air conditioning,” he said.
“The air conditioning picked up a smell from outside and it filtered through the building.”
Mr Eenjes said two or three people suffered headaches because of the smell.
“Once everyone was evacuated from the building and got some fresh air they all felt better," he said.
"The smell also disappeared from the building.
“When we first got to the scene we did pick up a carbon monoxide reading, but that also quickly went away.
“The building was declared safe a short time later.”
Mr Eenjes said someone from the air-conditioning company would be sent out to check the building in coming days.
Bendigo police Sergeant Mick McCrann praised CGU Insurance staff for their quick thinking.
“They have done the right thing. They have connected the emergency services,” he said.
“They also had an evacuation plan, which they used.”