The Department of Defence is investigating an alleged coronavirus quarantine breach involving a member of the Australian Defence Force.
Northern Territory Police say the 41-year-old man had recently returned from overseas and was quarantining in Darwin.
He allegedly left his designated accommodation at some point on Saturday before being caught and fined.
A Defence spokesman said the department was aware of the matter.
Defence takes its COVID-19 responsibilities seriously and follows the direction and guidance from relevant Commonwealth and State authorities," he said.
"Defence is currently investigating the matter."
While the vast majority of people required to quarantine in the NT do so under mandatory supervision at a facility in Howard Springs, alternative plans are approved on a case-by-case basis.
Police say the man came to their attention because of his aggressive behaviour, then returned to his accommodation.
They have not disclosed where he returned from or where he was staying, other than saying there were plans in place to prevent community contact.
People caught breaching their quarantine requirements in the NT face fines of $5,056, while businesses can be penalised $25,280.
It comes as the Northern Territory border today opens to people arriving from most of regional Victoria.
The NT Government is yet to set out a formal timeline for the border reopening to people from Melbourne and the Mitchell Shire, which remains a declared coronavirus hotspot.
