The outer panel of a double-glazed window in a fire exit at Maidenhead Mosque in Holmanleaze was damaged this morning.
Caretaker Nazir Amjad locked the mosque up at around midnight, and found the damage when he returned at 11am.
Small stones were found by the door.
Mr Amjad said: "We're lucky it wasn't any worse - there are much bigger windows they could have targeted."
Mr Amjad added that CCTV footage of outside the mosque had failed to pick up the culprits, meaning it was likely the vandals threw the stones from a distance.
Saghir Ahmed, the mosque's secretary, said: "I think it's obviously related to the horrific incident which took place in London yesterday.
"In the back of our minds, although we were hoping, we were expecting it.
"We were horrified like everybody else by what happened in London. These people who committed this crime, they might be expressing themselves as Muslim, but this is not the spirit of Islam."