Spain's air force sent a jet to pick up the four Cubans to transport them to an air base in Madrid, a foreign ministry spokesman said.
A rights group and Spanish media named the four as Pedro Pablo Alvarez Ramos, Omar Pernet Hernandez, Jose Gabriel Ramon Castillo and Alejandro Gonzalez Raga.
Spain earlier announced that Cuba would free seven of 59 dissidents imprisoned since 2003.
Leiva, who is a leader of a group of women relatives of jailed dissidents, said there was no word on the three other dissidents that were expected to be freed.
The release of the dissidents, the first since August, was based on health concerns and negotiated by Spain.
Miguel Angel Moratinos, the Spanish foreign minister, said: "The decision was made unilaterally by the Cuban authorities and we are very satisfied."
The four dissidents were arrested in a political crackdown ordered by Fidel Castro, the Cuban leader, in March 2003, which imprisoned 75 of his opponents for up to 28 years.
The release of the four is believed to be the result of human-rights talks held in Madrid last week by the Spanish and Cuban governments.
Sixteen others, including Chepe, have been freed on health grounds.
Chepe said the latest releases were a step in the right direction by Raul Castro, Cuba's acting president, who has been running Cuba since Fidel Castro was sidelined by illness in July 2006.
Fidel Castro has not appeared in public since.
Cuba's main rights group, the illegal but tolerated Cuban Commission for Human Rights, says there were 234 political prisoners in Cuba at the end of 2007, down from 283 a year earlier.
Cuba recently announced it would sign the UN International Covenant on civil and political rights and a similar pact on economic and social rights by March.
This would oblige Cuba to accept regular UN monitoring of its human rights record starting in 2009.
The Cuban government denies holding any political prisoners and labels dissidents "counter-revolutionary mercenaries" on the payroll of the US.