The Sun said that shoppers in Hertfordshire spotted the rapper in the shop, where he takes donations and helps staff.
"A few people have been shocked to see Dappy in the shop. He's been getting on with it though," a source was quoted as saying.
The pop star, whose real name is Costadinos Contostavlos, was given a six-month sentence, suspended for 18 months, in connection with a brawl at a petrol station.
He was also ordered to carry out 150 hours of community service.
He tweeted in May: "50 hours of community service done. Another 100 to go. Staying low until then."