In a statement, the WHO said the deaths had occurred in January to March, with 151 suspected cases recorded.
There was, it said, a "serious risk of further spread of the disease" in DRC.
The acute, mosquito-borne viral disease has killed 225 people in Angola and infected about 1,600 there.
The WHO said the DRC health authorities had set up a national committee to respond to the outbreak, including "screening and sanitary controls" on the country's borders.
People travelling to Angola will now be vaccinated against the disease, it added.
The WHO statement says that the DRC's health ministry has in addition activated a contingency plan which includes more community engagement to fight the disease and better training of health workers.
Yellow fever is a virus that can cause bleeding, jaundice and kidney failure, It is spread by mosquitoes, usually the Aedes aegypti mosquito, the same species that spreads the Zika virus.
It is endemic in tropical regions of Africa and South America.
A vaccine can prevent infection but there is no specific drug treatment for people who are infected.