The bodies of US citizen Michael Sharp and Swedish national Zaida Catalan were discovered in the central Kasai region, a government spokesman said.
They were abducted two weeks ago after going to Kasai to investigate reports of abuses after local rebels took up arms.
Some 40 police officers were found beheaded in the region at the weekend.
Congolese government spokesman Lambert Mende confirmed reports of the discovery to the BBC.
