Chris Williams apparently has a forgetful mind ... because that's allegedly why the R&B singer ended up in handcuffs for stealing.

Sources tell us the incident went down Saturday at a Kohl's in McDonough, Georgia where Chris walked in with a tote bag and wearing a baseball cap. We're told he went to the back of the store and grabbed a pair of JBL headphones ... priced at $99.99.

We're told he threw the headphones into his bag and tried walking out. When security stopped him, we're told Chris said he simply forgot he bagged them.

By then, cops were called and arrested him. The "I'm Dreamin'" singer was arrested and booked for petty theft, a misdemeanor. He was released after a couple hours.

We've reached out to Chris for comment, so far no word back.