Maduro on Saturday visited a government-run market, promoting vegetables and other foods at cheap prices. In other appearances this past week, he presented new public housing and inaugurated a school.
Opposition leader Henrique Capriles said in a message on Twitter: "Maduro campaigning, be prepared!" Other opposition politicians have questioned Maduro's higher profile, saying it suggests an effort to promote him.
Maduro expressed confidence that Chavez will return home.
Before his latest cancer surgery, Chavez said that if his illness cuts short his presidency, Maduro should run in a new election to take his place.