The footage was recorded by a passenger on the Aerobus service that connects Terminal 1 of Barcelona's El Prat airport with Plaça Catalunya in the heart of the city.
The bus was said to be completely full of passengers.
One of those on board spotted the driver counting money instead of paying attention to the road and began to record him.
When the driver began to engage in a text chat on his phone, some passengers asked him to stop but were ignored.
It was only when the driver saw in the rear-view mirror that he was being filmed that he put down the phone and began to concentrate on controlling the bus.
The head of communications for the bus company SGMP, Manel Plasensia, described the incident as "regrettable" and "unusual", according to local daily El Periodico.
"This behaviour is considered as serious misconduct in our driver manual," he said, and apologized to the passengers.
SGMT has opened disciplinary proceedings against the driver.