The eight have been held by Mai Mai armed militia since last Friday near the remote area of Fizi, in South Kivu province, it said in a statement.
"We demand that the group holding our personnel release them as quickly as possible," said Franz Rauchenstein, head of the ICRC delegation in the country.
An ICRC spokeswoman in Geneva said she could not provide any further details about the staff or whether the agency was in contact with the Mai Mai.
The ICRC maintains a permanent presence in South Kivu province in Bukavu, Uvira, Marungu and Fizi. Access is difficult owing to the remoteness of the region, logistical challenges and security conditions, it said.
The area has been the scene of violent clashes which have resulted in the displacement of thousands of civilians in recent months, it said.
