The president told reporters he underwent a lung X-ray on Monday after experiencing fever, muscle aches and malaise.
As of Tuesday, his fever had subsided, he said, and he attributed the improvement to hydroxychloroquine.
He took over after his predecessor, a doctor and health care consultant, quit in protest over Bolsonaros support for hydroxychloroquine.
Bolsonaro supporter Silas Ribeiro said on the streets of Rio that the president is correct in saying the dangers of the virus have been exaggerated.
Unlike Britain's prime minister, who moderated his rhetoric after testing positive for the virus, Bolsonaro will probably not change his stance, said Leandro Consentino, a political science professor at Insper, a university in Sao Paulo.