"He's getting better each day," the younger Castro said to news media at the opening of an international book fair on Thursday. "He's exercising much. He has a telephone at his side and uses it a lot."
Last week, Cuba released a new official video that showed a more robust image of the bearded leader a half-year after he was sidelined with intestinal surgery.
Fidel Castro had ruled Cuba for nearly 48 years when he announced on July 31 that he had undergone surgery and was temporarily ceding power to his brother. Since then, Raul Castro has appeared in public and given speeches only when he has deemed it necessary, the AP reports.
On Thursday, Raul made a surprise appearance at the annual book fair - an event his 80-year-old brother had often attended in past years.
"He's consulted on the most important questions," Raul Castro said of Fidel. "He doesn't interfere, but he knows about everything.
"Luckily, he doesn't call me much," he joked, usually instead calling on Vice President Carlos Lage and Foreign Minister Felipe Perez Roque.
The 75-year-old defense minister traded in his typical olive green uniform for a gray jacket over a pair of blue pant for the event at a Spanish fortress across the bay from Havana.
Arriving at the opening in a small bus, the younger Castro was accompanied by Culture Minister Abel Prieto.
He greeted other key members of Cuba's caretaker government, including Perez Roque, Lage, and National Assembly President Ricardo Alarcon.
Raul Castro's appearance at a purely cultural event was seen as highly unusual, and it was not immediately clear if it would mark the emergence of a new, more public persona as his older brother remains sidelined due to illness. His informal comments to the press were the first since he assumed provisional power.
In past years, the older brother had often enjoyed attending the opening of the book fair, arriving last year with his good friend and ally, President Hugo Chavez.
Fidel Castro's illness remains a state secret, but Cuban officials have denied past U.S. government reports that he suffered from fatal cancer. A Spanish newspaper last month that the leader had diverticular disease, a weakening of the walls of the colon common in older people, the AP reports.
A new official video aired on state television Jan. 30 showed a stronger Fidel Castro who looked like he had gained weight during his convalescence. He looked far more gaunt and pale during a previous video released in late October.
In recent days, Chavez and other Cuban officials have made encouraging assessments about the elder Castro's health. Venezuela's ambassador to Cuba Ali Rodriguez Araque said earlier Thursday that he had resumed eating after a long period of being unable to ingest solid foods.