Police spokesman Roman Hahslinger said the masked man got on the 86A bus at the Vernholzgasse stop at around 7.15am and started shouting loudly.
Wednesday was a public holiday in Austria and at this time the driver was alone in the bus, and was taking a short break. He told police he couldn't understand a word the man said.
The creepy clown began hitting the screen on the driver's cab, and he then smashed the video information screen at the front of the bus. After that he got off the bus and ran away. The driver immediately called the police but they couldn't find the clown.
The bus driver had to take the rest of the day off work as he was in shock.
On Sunday a 19-year-old woman who was out horse riding was injured after a man dressed as a clown jumped out from behind a tree and blew a party horn, spooking her horse. She fell off and suffered cuts and bruises.
The clown ran off without checking to see if the woman needed help. Police say he could be charged with causing bodily harm.
Several other people in Austria have been injured in attacks by masked assailants in the lead-up to Halloween, who have obviously been inspired by the so-called creepy clown trend. Police have issued several warnings against wearing a clown mask.
In Germany, police have reported at least 370 creepy clown incidents, ranging from clown sightings to attempted and actual attacks with knives or other weapons.