Brent died Nov. 4 from bronchial pneumonia, Elouise Rawlins said in a telephone interview from her home in Oakland, Calif.
Rawlins said she learned of her brother's death through telephone calls and messages from friends and acquaintances, but has not received official word from the U.S. or Cuban governments.
Rawlins said she had not seen her brother since he used a handgun to hijack TWA Flight 154 from San Francisco to Havana on June 17, 1969, but said they stayed in contact through e-mails and telephone calls.
"We didn't even know he was ill," Rawlins said. "I don't know about the burial or anything — just that he passed away."
The telephone rang unanswered Friday at Brent's Havana home, which he shared with his wife, travel writer Jane McManus, until her death last year. They had met and married in Cuba.
Brent lived a relatively isolated life during his nearly four decades in Cuba, spending much of his time in his later years listening to his beloved jazz music collection in his apartment.
In a 1996 interview with The Associated Press, he said he missed the United States and the American black community. But he was unwilling to return home to face certain life imprisonment for aircraft piracy and kidnapping, and had resigned himself to never seeing his country again.
"I miss my people, the struggle, the body language," Brent told the AP. "The black community in Cuba is very different."
Still, he said he had no regrets about hijacking the plane. "I was a soldier in the war for black liberation," he said.
A decade ago, Times Books published his memoirs, "Long Time Gone," which told of his coming of age on Oakland's streets and of joining the Black Panthers when he was 37, rising to become a bodyguard for leader Eldridge Cleaver.
The Black Panther Party for Self-Defense was founded in October 1966 in Oakland, by Bobby Seale and Huey P. Newton. They called for an end to police brutality in the black community, and carried guns as they patrolled the city documenting police behavior.
In his book, Brent chronicled a July 1968 police shootout in which two police officers were critically wounded. Cleaver ordered him kicked out of the revolutionary group.
To avoid trial the following year, Brent used a .38-caliber handgun to hijack the plane to Cuba, where he believed he would be treated sympathetically as a militant black leftist. None of the 76 people aboard the Boeing 707 was harmed.
He also told of stepping off the plane in Cuba to be immediately hustled away by Cuban police.
Although never formally convicted, he spent 22 months in an immigration jail while Cuban authorities tried to figure out what to do with him. Eventually they let him stay to live out his exile.
Brent earned a Spanish literature degree from the University of Havana and taught English at junior and senior high schools, but he never became a Cuban citizen.
"I am an American, an African-American, a black man," he said in the 1996 interview with the AP. "And my fight was always in the United States."