Boston Police are investigating an alleged armed robbery on Tuesday evening in which a male victim was held up at gunpoint near the corner of Mayfield Street and Dorchester Ave. The incident happened at about 7:50 p.m. The victim told police that two young men accosted him as he was walking on Mayfield Street in the direction of Pleasant Street. The victim lost his wallet, including $130 in cash. The suspects, described as black males in their 20's approximately 5'6"-5'8, fled towards Dorchester Avenue, according to the police report.