Flight AI 131  travelling to London on Wednesday was flying over Iran when someone on board said they spotted the rodent, reports said.
Passengers continued their journey on a replacement aircraft some time later.
Air India has said that the plane will be fumigated and the presence of a rodent was being investigated.
Rats occasionally get on board aircraft along with catering and other supplies but can pose a serious technical as well as a health hazard if they chew through wires.
The airline said that "though the presence of the rodent was not confirmed," the decision to abort the flight was precautionary and in the interests of passenger safety.
It is not the first time a rat sighting has been reported on an Air India jet this year, with one of their aircraft forced to return to New Delhi during a flight to Milan in July because of a rodent.
It is the latest setback to hit the state-owned airline, which has had to cut costs to improve its financial health.
Earlier in December, an Air India technician was sucked into an aircraft engine and killed at Mumbai airport.
A plane travelling from Mumbai to London was forced to turn back mid-flight after a rat was spotted on board, local media report.