The man died of Lassa fever, New Jersey health authorities and the US Centers for Disease Control and Prevention (CDC) said.
Although the virus triggers hemorrhagic symptoms, it differs from Ebola, which has caused an epidemic in West Africa over the past year and a half.
The US man, who was not identified, had traveled from Liberia to Morocco before arriving at New York’s John F. Kennedy International Airport on May 17.
He was hospitalized on May 21, after an initial hospital visit during which doctors failed to identify the virus.
It was only early Monday, hours before his death, that blood samples analyzed by the CDC tested positive for Lassa fever.
Tests for Ebola and other hemorrhagic fevers were all negative.
The patient was in an isolation unit at the time of his death, according to the CDC.
The CDC said it was working to identify those who came in contact with the patient, and that his close contacts will be monitored for 21 days to see if any symptoms emerge.
While common in West Africa, Lassa fever is very rare in the United States, where no person-to-person contagion has yet been reported.
The New Jersey case was the sixth known of its kind since 1969 involving a traveler returning from Africa, without counting those in recovery.
The last case was in Minnesota last year.
The virus is carried by rodents and transmitted to humans through contact with the urine or droppings of an infected rodent.
It is rarely transmitted among humans, through direct contact with the blood or bodily fluids of an infected person, through mucous membranes or sexual contact.
There are 100,000 to 300,000 cases per year in west Africa.