The graffiti, found on Sunday morning, were being “investigated by the national security agency,” a police spokesperson told Agence France Presse (AFP) on Monday, February 2.
The attack came ahead of the country’s first anti-Islam protest planned on Monday evening.
The protest is organized by an offshoot of PEGIDA group, which has drawn thousands of supporters on the streets of the German city of Dresden is recent months.
Small “Patriotic Europeans Against the Islamisation of the Occident” offshoots have also sprung up in other German cities and in European countries including Denmark, Switzerland and Spain.
The Vienna march in the city center was expected to attract fewer than 300 people. A counter-demo was also planned, with 1,200 extra police on duty in case of trouble.
The mosque attack is the last in a series which kicked off last December.
In one attack, unknown culprits left a pig’s head and intestines in front of the door of another mosque in the capital. A street sign was changed to read “Shari`ah Street” in September.
This weekend four swastikas and the word “Hitler” were found drawn and etched on walls on the former Nazi concentration camp Mauthausen.
On Saturday night two men were assaulted in central Vienna by four others shouting anti-Semitic slogans such as “Scheissjuden” (“shitty Jews”), media reports said.
Austrian Muslims are estimated at about half a million or nearly 6 percent of the European country's 8 million population.
In Vienna, Islam is the second-largest religious grouping, after Roman Catholicism.