Castro said he still participates "in many of the important decisions" made by Cuban leaders including his brother, Raul, who Fidel made interim president in late July, Granma newspaper reported Sunday.
For weeks rumors had circulated that Fidel was dead due to complications from his gastro-intestinal surgery.
"This is what I wanted to point out to you," Castro said, in a translation made by the Miami Herald. "Now, when our enemies prematurely have declared me to be moribund or dead, I am pleased to send to my compatriots and friends worldwide this small filmed material."
Castro turned 80 this year but plans for an elaborate birthday celebration were postponed because of his illness. He was last photographed or filmed during a visit with Venezuelan President Hugo Chavez.