The cause of the crash was not immediately known.
Six other people were injured in the crash.
“A crisis taskforce is working at the crash site,” UN spokesman Martin Nesirky said.
A senior Congolese aviation official said the plane was travelling from Kinsangani to Kinshasa.
The UN mission in Congo, known as MONUSCO, includes more than 19,000 uniformed peacekeeping troops. The mission is charged with protecting civilians in the enormous Central African nation wracked by violence from a myriad of rebel groups and militias.
Congo has one of the worst air safety records in the world.