“So far there are 19 suspect cases, including three deaths and two lab-confirmed cases,” a WHO spokesperson in Geneva said via e-mail.
The first case was confirmed on Friday in Bas-Uele province in the north-east.
The WHO has said the outbreak appears to be limited to that remote area, and that there is no need for travel restrictions for the time being.
The Africa Centres for Disease Control and Prevention, a continent-wide mechanism to monitor disease outbreaks, said it had activated its emergency operational centre to monitor the situation in Congo.
The Central African country has suffered seven previous outbreaks of Ebola since the virus was discovered in the country in 1976.
The last outbreak, in 2014, left 49 people dead.
The West Africa were the worst, where it claimed more than 11,000 lives in 2014 to 2015.
The WHO declared Guinea, Liberia and Sierra Leone, the three countries that had been most effected by the epidemic, free of Ebola in 2016.
NAN reports that the GAVI global vaccine alliance said on Friday some 300,000 emergency doses of an Ebola vaccine developed by Merck could be available in case of a large-scale outbreak.
The vaccine, known as “rVSV-ZEBOV”, was shown to be highly protective against Ebola in clinical trials published in December 2016.
The vaccine is the first to prevent infection from one of the most lethal known pathogens, and the findings add weight to early trial results published in 2016
The vaccine was studied in a trial involving 11, 841 people in Guinea during 2015.
Among the 5,837 people who received the vaccine, no Ebola cases were recorded 10 days or more after vaccination.
In comparison, there were 23 cases 10 days or more after vaccination among those who did not receive the vaccine.
The trial was led by WHO, together with Guinea's Ministry of Health, Medecins sans Frontieres and the Norwegian Institute of Public Health, in collaboration with other international partners.
Since Ebola virus was first identified in 1976, sporadic outbreaks have been reported in Africa.
The 2013–2016 West African Ebola outbreak, which resulted in more than 11 300 deaths, highlighted the need for a vaccine.