Abraham Borbor was one of three doctors who received ZMapp in Liberia. He became infected with the virus when treating Ebola patients at the John F. Kennedy Medical Centre in the capital, Monrovia.
Information Minister Lewis Brown said Borbor's death late on Sunday came as a shock.
"He was walking around yesterday, and the doctors were hopeful that he would make a full recovery," said Brown.
The other two doctors, a Nigerian and a Ugandan working in Liberia, are still undergoing treatment, according to the government.
Two American health workers, Kent Brantly and Nancy Writebol, who had contracted Ebola in Liberia, were discharged last week from a hospital in Atlanta in the United States, where they had been treated with ZMapp.
Spanish priest, Miguel Pajares, however, died from Ebola in a Madrid hospital after his evacuation from Liberia, despite receiving ZMapp.
The Democratic Republic of Congo confirmed on Sunday its first two cases of Ebola, in the country's north-west, making it the fifth African country to be affected by the outbreak.
The Ebola death toll in the West African countries of Guinea, Sierra Leone, Liberia and Nigeria was 1,427 on August 22, with a total of 2,615 suspected or confirmed cases, according to the World Health Organization (WHO).
The disease is transmitted through contact with blood and other bodily fluids.
DPA