Oswaldo Paya, 60, was travelling near the city of Bayamo, in the eastern province of Granma, when the accident happened, they said.
He is known as the founder of the Varela Project – a campaign to gather signatures in support of a referendum on laws guaranteeing civil rights.
Oswaldo Paya was seen as a key spokesman for Cuba’s small opposition.
A Catholic church official in Bayamo told AFP that a local hospital had told him and other activists that Oswaldo Paya was dead, and had shown them identification.
His death was reported on Twitter by prominent dissident blogger Yoani Sanchez, who described him as “irreproachable” and his death as a great loss to Cuba.
The circumstances of the accident are still unclear. A usually well-informed pro-government blogger says Oswaldo Paya’s car crashed into a tree.
A state media website said there had been a “regrettable traffic accident” that killed two Cubans, while two other people, one Swiss and one Spanish, were injured.
Oswaldo Paya’s death comes after another prominent Cuban dissident, Laura Pollan, founder of the protest group Ladies in White, died last October.
In 2002, Oswaldo Paya won the Sakharov Prize – the European Union’s human rights award – for his work with the Varela Project, which was created in 1998.
In May 2002, he presented Cuba’s National Assembly with a petition of more than 10,000 signatures calling for an end to four decades of one-party rule.
He has since repeatedly delivered petitions to the body, including one in 2007 calling for an amnesty for non-violent political prisoners.
The Cuban government described him as an agent of the United States who was working to undermine the country’s revolution.
A devout Christian, Oswaldo Paya was also the founder of the Christian Liberation Movement, which campaigns for political change, civil rights and the release of political prisoners.
His influence is seen has having waned recently, with a new generation of internet-based activists, such as Yoani Sanchez, coming to the fore.
Born in 1952, Oswaldo Paya became a critic of the communist government as a teenager. In 1969, he was sent to a work camp as punishment.
Image source: Wikimedia Commons President-elect Donald Trump celebrated his election victory at the Ultimate Fighting…
Millions of voters across the US chose to return Donald Trump to the White House…
Donald Trump declares victory in the US election as he addresses jubilant supporters in Florida.…
Stocks around the world are rising as Donald Trump appears to be on the cusp…
Donald Trump has won Pennsylvania, North Carolina and Georgia and taken a lead over Kamala…
Quincy Jones, the celebrated musician and producer who worked with Michael Jackson, Frank Sinatra, Ray…