Paramedics found the man, who had sustained a severe head injury, in the Hochfeld district establishment's bathroom on Thursday evening. He died shortly thereafter at a nearby hospital, police said.
According to witnesses, several shots were fired at the “Bandidos Place” bar, which is a known meeting point for the similarly named Texas-based biker gang embroiled in a rivalry with the Hells Angels. Both are suspected of organised crime activities.
Police are searching for several vehicles that were seen fleeing the bar after the shooting. Investigators remain uncertain about whether the incident was related to the biker gang feud.
Biker violence in Europe has made headlines periodically in recent months in what police have called an escalating gang war. In August a member of a biker gang was shot and killed in Berlin's Hohenschönhausen district.