The incident, which the 26-year-old England international revealed on Twitter, happened late Friday afternoon.
No-one was hurt and Bent's Land Rover was not damaged.
A spokesman for Northumbria Police said: "At 5.08pm today, police were called to High Bridge in Newcastle near to the Groat Market to reports that a drinking glass had been thrown at a parked Land Rover.
"Officers attended the scene and inquiries are under way.
"No-one has been injured and there are no reports at this time of any damage having been caused to the car."
Bent, who scored in Sunderland's 5-1 defeat to Newcastle at St James' Park last month, has missed the last three games with a hamstring injury, but has returned to training and could play in Monday night's Premier League clash with Everton.