"It's a precautionary measure because of the violence. Just in case one would need an evacuation, you'd have fewer people to evacuate," said UN spokeswoman Radhia Achouri said on Thursday.
It was not clear how many staff would be evacuated.
Aid workers were already confined to the main town as all roads have been closed to travel because of banditry and clashes throughout the state, she said.
UN officials said on Wednesday the violence had hindered aid access to around 650,000 refugees in South and West Darfur states.
British aid agency Oxfam said it could not access any of its West Darfur camps by road and were concerned fuel for water pumps could run out, leaving tens of thousands of refugees without access to water.
Tens of thousands have been killed and more than two million forced from their homes in the Darfur violence, which the United States called genocide.
Khartoum denies genocide but the International Criminal Court is investigating alleged war crimes there.