"He is coming along well," Carlos Lage told reporters during a visit to Bolivia for the opening of a constitutional assembly on Saturday. "He's been made well by the operation and is recuperating favourably."
Brazilian newspaper Folha de S Paulo had reported that Cuban officials had told Luiz Inacio Lula da Silva, Brazil's president, that Castro had a malignant stomach tumour and his condition was worse than has been publicly admitted.
Lage said the 79-year-old leader could return to power "in several weeks".
Speculation about Castro's condition has been intense since he temporarily handed over power to his brother Raul while he underwent surgery for intestinal bleeding.
Havana has released no pictures of Castro and very few details of the surgery.
Raul Castro, the defence minister, also has not been seen in public since the handover.
Cubans were told on Tuesday in a statement attributed to Castro that most details of his health would be kept "a state secret" to prevent the island's enemies from taking advantage of his condition.