A Good Samaritan went to the aid of a man in a mobility scooter and was stabbed with a knife by a teenager, who was part of the group of youths harassing the elderly man, police allege.

Despite the wound, the Good Samaritan grabbed the boy and pulled him into a service station, where police were called and the alleged stabber was arrested on Tuesday.

The man on the mobility scooter was not injured.

Police said the 26-year-old man saw that three teenagers had accosted the elderly man behind a Waller Road service station in the Logan suburb of Heritage Park about 3.15pm.

It will be alleged a fight broke out between the younger man and the youths and a 15-year-old boy pulled out a knife and stabbed the man.

The alleged stabber was then restrained by the victim and detained until police arrived.

The man was taken to Princess Alexandra Hospital with non-life-threatening injuries.

A 15-year-old boy was charged with acts intended to cause grievous bodily harm and was due to appear in Beenleigh Children's Court on Wednesday.