The first of the new patients was a ten-year-old boy who lived with his parents and three siblings in Paynesville, a suburb east of the capital Monrovia, said Minister of Health Minister Bernice Dahn. Two direct family members have also since tested positive, officials said.
All six family members, as well as other high risk contacts, are in care at an Ebola Treatment Unit in Paynesville, she said.
Bruce Aylward, who leads the Ebola response for the UN World Health Organisation, said the patient had no history of contact with an Ebola survivor or victim.
Liberia has seen more than 10,600 cases of the disease and 4,808 Ebola deaths since it was first announced in March, 2014, WHO figures show.
The virus has killed a total of about 11,300 people in Guinea, Sierra Leone and Liberia. Sierra Leone was declared free of the virus on November 7 and Guinea has begun its countdown to the end of the virus.
The 42-day countdown to be declared Ebola-free starts when the last patient tests negative a second time, normally after a 48-hour gap following their first negative test.
