"His health is improving. He's recovering. He'll be back sooner rather than later. You're going to see more Fidel for a while," he said.
Castro temporarily handed over power to Raul Castro, his brother and Cuba's minister of defence, on July 31 while he recovers from surgery for intestinal bleeding.
Carlos Lage, Cuba's vice president and Venezuela's leader said on Sunday that Castro would return to work "in a few weeks".
"In a few weeks he'll be recovered and he'll return to his duties," Lage said while attending Bolivia's constitutional convention.
Cubans were told that most details of his health would be kept "a state secret" to prevent the island's enemies from taking advantage of his condition.
Officials have not disclosed Castro's precise illness or said what surgical procedure he has undergone.
Neither of the Castro brothers have been seen in public or appeared on radio on television since the July 31 announcement.
Castro supporters warn US against interference
Supporters of Castro have meanwhile urged the US not to interfere with the Caribbean island during Castro's absence.
On Monday over 400 intellectuals, politicians and human rights activists from across the world released an open letter warning the US not to try to force a change of government on Cuba.
"We demand that the government of the United States respects Cuba's sovereignty ... We must prevent a new aggression at all costs," said the letter which was released in Havana.
The letter was signed by seven Nobel Peace Prize winners, including Archbishop Desmond Tutu and Rigoberta Menchú.
Bush calls for democracy
George Bush, the US President, has said that Cubans "on the island" ought to decide their own post-Castro future, but added the US wished to see Cuba’s one-party Communist government replaced by a multi-party democracy.
"Our desire is for the Cuban people to choose their own form of government," Bush said from his ranch in Crawford, Texas.
The US has been opposed to Castro since he violently overthrew the island’s pro-US dictatorship in 1959.
In 1961 Castro's soldiers defeated a US-backed invasion by anti-Communists Cuban exiles who landed in Cuba's Bay of Pigs.