The missionaries travel to the West African nation on behalf of SIM USA, based in Charlotte, North Carolina. "It's very important to hear and understand that none of the returning missionaries are ill, none of them have the Ebola virus disease," said Stephen Keener, medical director of North Carolina's Mecklenburg County Health Department.
Some media have said there are three missionaries in quarantine.
Among them, apparently, is the husband of SIM missionary Nancy Writebol, 59, repatriated from Liberia last week after being infected by the disease and now being treated in isolation at Emory University Hospital in Atlanta.
The people under quarantine are "kept at home or in another situation that is controlled so they do not contact other people", Keener said.
In the case of Ebola, the risk lies in contacting bodily fluids, blood or vomit of someone suffering the disease.
Declared an international public health emergency by the World Health Organisation (WHO), the outbreak of the virus has claimed lives of more than 960 people in Liberia, Sierra Leone, Guinea and Nigeria.
At the petition of the WHO, the US Centres for Disease Control and Prevention has taken over the direction of the international mission to halt the advance of the Ebola outbreak in Africa.