The International Rescue Committee said it was "alarmed" that there were 33 new cases between October 1 and Tuesday, versus 41 cases during all of September.
The outbreak is centered in the city of Beni, where rebels killed at least 18 people in an attack last month, forcing health workers to suspend operations for several days.
"The current spike in Ebola cases and deaths is extremely worrying", said Michelle Gayer, IRC's senior director of emergency health.
World Health Organization has warned that the risk for Ebola's regional spread is "very high", pointing out that Congo's affected North Kivu and Ituri provinces share borders with Uganda and Rwanda.
According to the Congolese Health Ministry, the newest Ebola cases were reported this week along the border with Uganda. As a result, health officials say many infected people are afraid to come forward and seek medical treatment.
The WHO cited transport links and population movements as potential risk factors, while stressing that the global risk remained low. The spread of the virus to "red zones", where the threat of armed groups makes health efforts nearly impossible, is a major concern. More than 15,000 people have been immunized with a novel vaccine since this outbreak was declared on August 1. Though the Ebola outbreak in North Kivu province began on Aug 1 in Mblanka, activity has now moved to Beni as health workers fight a second wave of cases connected to people who refused vaccination or dodged case contact follow-up.Three cases tied to 1 clinicThree of the new cases involve children all seen at the same clinic in Butanuka district, Beni.