Arcos was a comrade of Fidel Castro in the early days of the revolution, but later imprisoned for criticising the regime.
He was "a symbol of the opposition, the dean of the opposition," said Marta Beatriz Roque, an opposition figure, who said she was told the news by Arcos's wife.
Arcos, the eldest of Cuba's dissidents, entered hospital on July 18, suffering from pneumonia and a urinary infection.
"He had pneumonia and died from respiratory failure," Roque said.
"He was in the hospital and he never went home, because his condition was very bad," said Roque.
Arcos's wife Teresita Rodriguez said recently that in the last weeks her husband had weakened considerably.
Arcos was a law student when he took part in the 1953 assault on the Moncada military base in Santiago de Cuba, the incident that sparked the Cuban revolution.
"He fought against (dictator Fulgencio) Batista and now he was fighting the tyranny of Fidel Castro," Roque said.
After the revolution triumphed in 1959, Arcos became ambassador to Belgium, but became increasingly critical of the regime and resigned in 1964.
He returned to Cuba and was imprisoned from 1966 to 1969, and again from 1982 to 1988.
In an interview with the AFP news agency three years ago, Arcos said he had no regrets.
"I followed the ideals that guided us in those times, which were to eliminate the Batista regime and re-establish democracy."
He founded the Cuban Pro-Human Rights Committee along with his brother Sebastian and two other dissidents, Ricardo Boffil and Elizardo Sanchez, in 1988.