Cuba saw rare public protests in July over rising living costs, food shortages and the continuing US embargo.
Cuban dissident, journalist and human rights campaigner Guillermo Farinas has been arrested on Friday, his family said.
His arrest on Friday comes three days before opposition figures plan to hold a protest that has been banned by the government.
“They arrested him today. They took him around 2:10pm [19:10 GMT],” Farina’s mother Alicia Hernandez told the AFP news agency.
She said her son is on antibiotics because of a urinary tract infection.
“An ambulance and two police patrols came and took him to the Arnaldo Milian Castro Hospital,” Hernandez said.
“They told me that tomorrow a prosecutor will visit him to charge him, but we don’t know what for.”
Farinas, 59, is a psychologist by training and has worked as an independent journalist and human rights activist. He won the European Parliament’s 2010 Sakharov Prize for Freedom of Thought.
Over the last 20 years or so, Farinas has undertaken 23 hunger strikes to protest the Cuban government, considerably damaging his health.
He is a member of the Patriotic Union of Cuba, the most active political opposition group in the country.
Farinas’ arrest comes before a planned opposition-led demonstration set for Monday to demand the release of political prisoners in Cuba.
The gathering has been banned by the island’s communist government, but organisers plan to go ahead with it anyway.
Government authorities allege the protest organisers are backed by Washington and are seeking to provoke a change in government.
President Miguel Diaz-Canel said his supporters were “ready to defend the revolution” in the face of “an imperial strategy (of the United States) to try to destroy the revolution.”
“We are calm, sure of ourselves, but attentive and alert, and we are also prepared to defend the revolution, to face any interventionist action against our country,” Diaz-Canel said in a television appearance on Friday.
“We are a revolution open to dialogue, to debate,” he added, “but we are a society closed to pressure, closed to blackmail and closed to foreign interference.”
Cuban officials, who deny the existence of political prisoners in the country, consider the opposition to be illegitimate and allege it is financed by the United States.
Unprecedented nationwide street protests rocked Cuba in July as people took the streets shouting “freedom” and “we are hungry”.
The protests left one person dead, dozens injured and 1,175 arrested. Half are still in jail, says the human rights group Cubalex.
The main organiser of the march on Monday, Yunior Garcia, said on Friday the authorities warned him he will be arrested if he goes ahead with plans to march by himself one day earlier.
“They even told me what jail they are going to take me to,” Garcia told AFP, insisting he will go on his solitary protest walk anyway.
“I am not going to hide.”
Garcia is a 39-year-old playwright who founded Archipielago, the group that is urging Cubans to take to the streets on Monday to protest against the government.
He says the goal of walking by himself in downtown Havana is to minimise the risk of violence.