Public broadcaster ORF reported on Monday that a local resident notified police of the incident at around 9:40 pm local time (1140 GMT) on Sunday evening. Police found the severed pig's head at the entrance when they reached the site.
The State Office for the Protection of the Constitution has now taken over the investigation.
The city has witnessed similar incidents in the past.
On the night of May 6, 2016, a man had attached pig head halves to the exterior of a mosque and spilled pig blood over it. He was arrested a short time later.
The man and two accomplices had been convicted in 2020.
In 2021, two members of the Austrian Army Counterintelligence Office were also charged in connection with the 2016 incident. They were accused of knowing about the attack but protecting their informants and not passing on their knowledge to the police.
The two individuals were sentenced to fines in January 2021 but had appealed the verdict. These proceedings are still ongoing.
Source: TRT World