He has not been arrested as he is not old enough to be tried in court but he has been detained and is being questioned. The Krone newspaper reports that the boy is just 12 years old, although police would not confirm his exact age.
Investigations into a 17-year-old terror suspect who was arrested in Vienna on Friday are continuing - but at a press conference on Monday police would not give any concrete details of what they have discovered so far. They did say that the young boy involved had been radicalised by a “hate preacher” and was in close contact with the 17-year-old.
Austria's director of public security, Konrad Kogler, said that officials received several tip-offs that suspected Islamic extremists were plotting an attack in Austria a few days before the arrest on Friday, in Vienna's Favoriten district.
They were able to identify a suspect, who was placed under observation, and security was raised in Vienna. On Friday they arrested him and searched several properties in Vienna and Lower Austria. Several computers and mobile phones were seized and are being analysed.
The suspect has been named as Lorenz K., born in Austria to parents of Albanian origin. He grew up in the small town of Neunkirchen, south of Vienna. Police say Lorenz K. was known for petty crimes and assault and that they believe he is part of an international network of Islamic State supporters.
When they found that the suspect was in “close contact” with other people in Germany they contacted the German authorities, who arrested a 21-year-old man in the western city of Neuss on Saturday.
Austria's director of public security, Konrad Kogler, described the radicalisation of Austrian-born teenagers as a “relatively new phenomenon in Austria”.
He asked parents and teachers to contact the authorities if they are concerned that a young person is in danger of becoming radicalised.
Karl Mahrer, the deputy head of the Vienna police, said that a 220-strong standby unit is ready in case of an emergency, but also stressed that "we can continue to live normally and should not feel insecure".
He added that whilst police are still investigating and until they know if attacks have actually been planned in Austria, security measures will remain high in Vienna and across the country, with an increased police presence in busy public places and transport hubs.
Police have asked people to call them if they see anything suspicious or notice bags left unattended - the number to call from within Austria is 133.
Media reports in Germany and Austria say that the 21-year-old and 17-year-old had experimented with making explosives in a flat in Neuss.
Austrian authorities said that Lorenz K., who turns 18 in the coming days, was transferred to the Justizanstalt Josefstadt prison in Vienna on Sunday afternoon.
The reports said that he possibly became radicalised while serving a year in prison from 2014-15 for assault.