Castro was shown holding a copy of Saturday's edition of Granma, the Cuban Communist Party daily newspaper, in a video aired on Cuban state television on Saturday.
In the video Castro said: "They've declared me moribund prematurely. But it pleases me to send my compatriots and friends this small video."
The Cuban leader, who temporarily stepped down from power in July following intestinal surgery, appeared thin and tired, but read the newspaper in a loud voice and was shown walking slowly but steadily in an unidentified room.
He had not been seen since mid-September, when photographs of him receiving world leaders at a summit in Havana were released.
Castro, who is 80, said his recovery would be prolonged and not without risk, but that "I am coming along just as planned. I'm not the least bit afraid of what will occur".
The Cuban government has treated Castro's ailment as a state secret, and rumours that he may have died had intensified in recent weeks.
He had not made a public appearance since July 26, a few days before he underwent surgery.
Castro called the suggestions of his death ridiculous and insulting, saying they were the work of his enemies.
He said: "Let's see what they say now."
The video came a day after Castro's close friend and ally Hugo Chavez, Venezuela's president, said the Cuban leader was walking and taking trips at night into the countryside.