Minister of works and transport Veikko Nekundi says tenants staying at the old tuberculosis hospital in Khomasdal, Windhoek, should vacate the space by 1 April.
The building is not suitable for occupation, he says.
This comes as government employee tenants staying in the building have complained about non-government employees occupying it.
The tenants say some government employees live in shacks while the old hospital is occupied by non-government workers.
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The building comprises 25 rooms occupied by Namibians and Angolans.
The Namibian in 2015 reported that the Ministry of Defence and Veterans Affairs told residents, including soldiers and police officers, to vacate the building, which they have not done.
Nekundi, however, says all occupants are there illegally.
"I have issued a statement for them to evacuate.
We are waiting on the attorney general to ensure legal eviction requirements are complied with. Namibia is governed by the rule of law," he says.
One tenant, a government employee, refers to non-government employees as "illegal tenants".
He says these tenants have damaged the property and are selling illegal substances from the building.
Some have erected illegal structures and have connected illegal electricity to these structures, he says.
"Some 13 rooms are occupied by members of the public, and there are many in the rooms.
This is a waste of government water and electricity as the Ministry of Health and Social Services is paying for it," the tenant says.
He says the people have stolen copper wire, doors, fences, metal poles, and a generator.
Some police officers who have retired are renting out their rooms to the public, the tenant claims.
The Namibian visited the old hospital on Tuesday.
It reeked of alcohol, with some tenants sleeping in the hallway, and illegal structures visible behind the building.
Occupant Maveerepi Hepute, who stays in the building with his wife and child, says the Ministry of Health and Social Services gave him a room at Windhoek Central Hospital, which is too small.
He says the old TB hospital has become unsafe for children, calling on the works ministry to remove non-government employees.
"The government should remove these people.
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State employees are sleeping in shacks, while government accommodation is occupied by non-government people," Hepute says.
The old TB hospital was initially intended to be a N$450-million military hospital, but construction could not commence due to occupants refusing to leave.
