The unidentified driver has now been suspended by Rome's TPL transport company while it investigates the incident.
He told Il Messaggero he “needed the scooter to get home”.
Passengers were kicked off the bus after the driver announced: "The bus won't go. Everyone off,” reported La Repubblica.
Passengers said the driver then went to collect his a Honda Silver Wing 400 scooter, which was parked nearby.
They had been on board the number 982 bus operated by Roma TPL, the capital's suburban bus company, waiting to set off from the Quattro Venti station in the Monteverde area.
One passenger described the driver, who wasn't in uniform, as seeming "agitated and nervous” as he struggled to get his scooter on board.
After suspending the driver, Rome's TPL transport company said he now has three days to come up with an explanation for using the vehicle "improperly".
Rome's buses and other forms of public transportation frequently make headlines for all the wrong reasons.
Last week dozens of people were injured when a bus crashed into a tree in the city, and recently there were reports of a bus ticket inspector scamming tourists and two buses bursting into flames within 24 hours of each other - bringing the city's total number of bus fires in 2019 to a shocking total of 24.
Other causes for concern include ceiling collapses at metro stations and train doors failing to close. The city's well-documented transport woes are regularly exacerbated by strike action.