The 26-year-old rapper was performing at the Shoreline Amphitheatre in Mountain View, California, when the victim was gunned down backstage at around 11pm.
A source told TMZ.com: ''The victim was shot backstage and was hit at least five times.''
The emergency services rushed to the scene after receiving a high volume of calls about the incident and the 38-year-old man was taken to a local hospital, where he later died of multiple gunshot wounds. Mountain View Police spokeswoman Shino Tanaka said officers are currently investigating the tragic incident and are appealing for eye witnesses.
She said: ''It is an active investigation, so what we're looking for right now is to get the public's assistance. Anyone who was at the concert, who was backstage, who has any photos or videos of anything leading up to that incident around 11 o'clock yesterday evening.''
The victim's identity has not yet been released. It is not known whether Wiz - whose real name is Cameron Thomaz - has any connection to the victim or the shooter as he is yet to comment on the incident.