Adan Chavez made the remarks in a statement published on Saturday.
“Reports that the president is in a coma and that the family is discussing ending life support are totally false," the president’s brother said.
On Friday, Venezuelan Vice President Nicolas Maduro flew to Cuba to visit the ailing president.
"I'm leaving for Havana to continue that work of visiting the family, meeting with his medical team, visiting our commander president," Maduro said on television in Caracas.
The 58-year-old Venezuelan president traveled to Havana on December 10 for a fourth operation after his cancer reappeared, despite a year and a half of treatment.
In late March 2012, Chavez began radiation treatment in Cuba after an operation in February 2012 that removed a second cancerous tumor from his pelvic region. Chavez’s first tumor, which was baseball-sized, was removed in June 2011, and then he received chemotherapy.
Chavez, who came to power in 1999, was reelected to a new six-year term in October.