The men were riding in an armored vehicle in the Heglig oilfield area when they were stopped by Sudanese forces for "suspicious activities," an unidentified Sudanese military spokesman told the BBC.
The men, from Britain, Norway, South Africa and South Sudan, were flown to Khartoum for questioning, he said.
There has been fighting over the Heglig area since South Sudan gained independence from Sudan last July.
The Norwegian man, identified as John Sorbo, 50, is a member of the Norwegian People's Aid charity and a veteran of landmine removal, the group said Sunday in a statement.
"Our main priority now is to ensure that Sorbo and his colleagues are safe and to assure their rapid release," Per Nergaard, head of the emergency preparedness, said. "We are working closely with the Norwegian Foreign Ministry and our U.N. partners to assure this."
The other three were employees of a South African company working on a United Nations ordnance removal contract, the BBC said.