The Community Security Trust and police are investigating an incident at Orli kosher restaurant in Edgware, north-west London.
Eyewitness accounts posted on Twitter initially suggested shots had been fired from a car driving past.
The incident is believed to have taken place at around 5.30pm.
Pictures showed a shattered window but people could be seen still inside the restaurant.
Police at the scene said the incident was not terrorist related.
It was suspected that the damage had been caused by marbles or similar projectiles, possibly fired from a catapult.
No customers were in the restaurant when the incident occured and there have been no injuries reported.
CST said in a tweet: “We are aware of reports of a shot fired at kosher restaurant in Edgware. CST is on site, no injuries, not clear what type of weapon used.”
CST later issued an update saying an initial investigation suggested a firearm had not been used, and that the incident could be linked to a non-antisemitic incident in the area.
Volunteers from Shomrim security group are also at the site in Hale Lane.
Barnet Police said there had been four incidents of "windows being randomly shattered, possibly by marbles" and local officers were continuing their investigations.
Scotland Yard said a truck, a house and a shop were also believed to have been hit.
"We do not believe it to be gunfire," a Metropolitan Police spokeswoman said.
The restaurant remained open on Wednesday evening.
A member of staff said: "There is nothing to worry about. Everyone should relax."
To get more news, click here to sign up for our free daily newsletter.