Ricardo Alarcon told a US radio station he had met Mr Castro on Tuesday and discussed the impact of his ill-health on the country.
Mr Castro temporarily handed power to his brother, Raul, on Monday for the period of his recovery.
Neither of the two men has been seen in public since then.
In another development, the White House advised Cubans not to make the sea journey between the island and the US.
Correspondents say the situation in Cuba is calm, but security has increased.
Mr Alarcon told Democracy Now radio that he had spoken to the 79-year-old president on both Monday and Tuesday.
"He is perfectly conscious, very good speech as always," he said.
"We talked for over a half an hour on many things going on in the world, the impact that the announcement has had."
The Cuban speaker said he expected Mr Castro to have a "normal period of recovery" after his surgery.
The BBC's Stephen Gibbs reports that the whereabouts of Raul Castro is a question which is beginning to be asked around the streets of Havana.
Although for the last two days the Cuban defence minister has been the acting president, he has made no public appearances and released no statements.
As far as most Cubans see it, our correspondent notes, it is still his elder brother, Fidel, who is in charge here albeit from his sick bed.
'I feel fine'
Cuban state TV earlier quoted Fidel Castro himself as saying in a statement that he felt "fine".
Earlier the Cuban leader, who turns 80 this month, was quoted as saying that a punishing schedule in recent weeks had affected his health.
It is not clear whether he is in hospital or recovering at home.
The latest statement expressed gratitude for the good wishes Mr Castro had received from around the world, and urged Cubans to maintain their daily routines.
"Everyone needs to struggle, and work," he is quoted as saying.
This is the first time Mr Castro has relinquished any of his duties as head of the communist state since he came to power in 1959.
Fidel Castro has been among the world's longest-ruling leaders, outlasting nine US presidents.
Source:BBCLast Mod: 20 Eylül 2018, 18:16