Miguel Valdes Tamayo, 47, freed on Wednesday morning, was the second of 75 opponents jailed last year in a crackdown on dissents to be released on health grounds.
Authorities on April 14 set free human rights activist Julio Antonio Valdes so he could undergo a kidney transplant.
"This took me by surprise. I did not expect to be freed," Valdes Tamayo, who was serving a 15-year term for sedition, told Reuters at his Havana home.
He said the government might be planning to release the rest of the 75 dissidents, whose one-day trials and sentences of up to 28 years prompted international condemnation and a freeze in diplomatic relations with the European Union.
Leonardo Bruzon Avila, Emilio Leyva, Lazaro Rodriguez and opposition journalist Carlos Alberto Dominguez were released on Tuesday after 27 months in prison without trial.
The four were arrested on Feb. 22, 2002, and charged with inciting public disorder for trying to hold memorial ceremonies honoring four Florida-based Cuban exiles killed when Cuban fighter jets shot down their two small planes in 1996.
"They told me to go home and stay out of trouble," Leyva, 38, said at his home. "But they have no moral authority, because they jailed me arbitrarily."
International rights groups campaigned for the release of Bruzon, 49, a former librarian, after he began a hunger strike to demand a trial. US President George W. Bush mentioned him last year in a speech on Cuba.
Bruzon's health deteriorated in prison, where he went on hunger strike four times. He weighed 39 kg in April when he was transferred to a hospital, he said.
Bruzon vowed to keep fighting. "I want to continue fighting for the defence of human rights in Cuba," he said on Tuesday.
"These releases are a positive step, but there is no reason to believe the government has dropped its ultra-repressive approach toward its opponents"
Leyva and Rodriguez belonged to the small Pro Human Rights Party, which is affiliated with the Andrei Sakharov Foundation, a rights group named after the former Soviet dissident.
Cuba labels all dissidents as "counter-revolutionaries" on the payroll of the United States. The arrests ordered last year were the toughest crackdown in decades.
Another 16 have been jailed in the last two months. Veteran Cuban rights activist Elizardo Sanchez said the decision to free the five, made at the highest level of the Cuban government, did not indicate any change in policy.
"These releases are a positive step, but there is no reason to believe the government has dropped its ultra-repressive approach toward its opponents," Sanchez said. He said more than 300 people remain imprisoned in Cuba for political reasons.