The woman, who did not want to be named, said the bus was on William Jones Drive when the incident happened. The bus driver stopped and rang the depot to report the incident before continuing on the route.
The woman said she enjoyed travelling on CityLink buses.
"I can't speak highly enough of the bus drivers and the service. Drivers shouldn't have to put up with this sort of stuff ... the children should be in school."
There were two other reports of rocks being thrown at buses in July and August, one of which smashed a window where a woman and her granddaughter were sitting. Northland Regional councillor and deputy chairman of the council's transport committee Paul Dimery said the stone throwing incidents had been reported to police.
"It's serious because of the potential it could cause. Imagine if a rock hit a passenger or distracted a driver enough to cause a crash?"
Mr Dimery said the incidents were becoming more frequent over the past six months and had escalated from eggs to rocks. The incidents were mainly happening in Otangarei, Raumanga and Onerahi.
"It's a small minority who are causing trouble and the community deserves this essential bus service."
Mr Dimery said the representatives from the bus company, NRC, WDC and police had met Otangarei leaders last month looking for solutions. The result was an open day where the community could meet the bus drivers. The bus drivers were all supportive of the idea.