Robinson, 73, joined other former players at the Charm City Heroes event in suburban Baltimore Saturday, thanking fans, some of whom sent get-well cards to the Hall of Fame player, The Baltimore Sun reported.
Friday was "the first time I've been out since I got home from the hospital a little over a week ago," Robinson told the newspaper. "I'm getting stronger every day."
Robinson was admitted to Greater Baltimore Medical Center in March after he developed an infection.
The 16-time Gold Glove winner was treated for prostate cancer in 2009 but has since remained cancer-free.