Rep. Trey Radel (R., Fla.) plans to step down from Congress on Monday after being arrested on a cocaine-possession charge at a Washington restaurant last year, a spokesman in his office said.

Mr. Radel, who represents an area of Florida that includes Naples and Fort Myers, was facing an investigation from the House Committee on Ethics over the arrest and subsequent guilty plea for cocaine possession. The congressman was arrested after trying to purchase the drug from an undercover police officer. He later pleaded guilty and received a year of probation.