A man is accused of robbing two people, including a teen, who were riding CTA Red Line trains on the South Side last week.Jemaal Muhammad, 20, of DeKalb, is charged with two felony counts of robbery, one felony count of aggravated robbery and one misdemeanor count of theft, Chicago police said.On Dec. 29, Muhammad was allegedly among the offenders who robbed a 15-year-old boy who was riding a train in the first block of West 95th Street, and a 44-year-old man riding a train in the first block of West 79th Street, police said.Muhammad was arrested Tuesday in the Loop. He was scheduled to appear for a detention hearing Wednesday. Court information wasn't immediately available.