The fire was discovered at 4am at 250 Middleton Rd.
It caused moderate damage to the basement and interior of the Dunedin property.
The house was seized by police following "Operation Rocket" in April, which targeted the activities of the Mongrel Mob in Dunedin.
Days after being confiscated by the Crown, the house was burgled while being guarded by a security firm.
It is still painted in Mongrel Mob colours and has the letters "MMM" on the fence beside the letterbox.
Fire Safety investigator Mike Cahill, of Invercargill, said at the scene on Saturday that it was too early to determine the cause of the fire.
"We're still investigating, but it looks like it started in the basement and spread to the wall of the house.
"There's also a little bit of damage inside.
"We're still looking to see if accelerants were used," he said.
"At this stage, it's being treated as suspicious and is being investigated by police."
Detective Jo McLaughlan, of Dunedin, said the property was being treated as a crime scene and that the cause of the fire was being investigated.
Dunedin police guarded the property over the weekend.
The fire was attended by units from the Lookout Point and St Kilda fire stations.
