On its online inmate locator, the bureau said Gonzalez or Ruben Campa -- the alias he used in the United States -- was freed from the low-security federal prison in Safford, Ariz.
Gonzalez, who spent 15 years behind bars, will be sent back to Cuba as soon as possible, CNN reported. He is likely to get a warm welcome in Havana.
Rene Gonzalez, who became the first of the "Cuban Five" to be released last year, has been involved in a campaign to free the other four.
"Of course, he will need a need to rest," Rene Gonzalez said last month of Fernando. "Then I hope he will take up the fight for our three brothers."
The five were convicted of failing to register as foreign agents and using forged documents. Cuban officials said they were in South Florida to stop terrorist attacks, while the United States described them as an undercover espionage network.
The group is known to have targeted Brothers to the Rescue, an exile group that sent small planes to drop leaflets on Cuba. A Brothers to the Rescue plane was shot down in 1996 by the Cuban air force.