Nabiam, Interior Minister Botche Cande and two other ministers were diagnosed on Tuesday and have been quarantined at a hotel in the capital Bissau, Health Minister Antonio Deuna told journalists.
He did not provide details of the officials' condition or treatment, but warned the country's rate of infection could rise.
The West African nation has so far confirmed more than 70 cases and one death - a senior police commissioner.Nabiam came third in last year's presidential election and was selected by the eventual winner, President Umaro Sissoco Embalo, to be prime minister in late February.