The court sentenced him to a minimum of eight months in detention with another 16 months of his sentence suspended.
Born in Turkey, he had been in Austria since 2007 and was arrested in October.
Prosecutors said he had contact with supporters of Islamic State (IS) and al-Qaeda, with the aim of going to fight in Syria.
The boy had been facing up to five years in custody and prosecutors said they would decide in the coming days whether to accept the decision.
Austria, like several other European countries, has struggled to stop the recruitment of teenagers by IS. A 16-year-old girl was facing charges in Vienna on Tuesday of supporting IS.
The boy, due to turn 15 shortly, was accused of having ties to terrorist groups and obtaining instructions on how to make an explosive device.
Before the trial began behind closed doors in the town of St Poelten, west of Vienna, his lawyer Rudolf Mayer told reporters his client would plead guilty.
According to Austrian media, his mother had tried to prevent him from being lured by Islamist propaganda, sending him away to his uncle in Germany last year.
But he was arrested last October, when police said he had looked into buying chemicals for a bomb to be detonated in public places such as Vienna's Westbahnhof station.
He was eventually released but returned to custody earlier this year after he broke his bail conditions and tried to recruit a 12-year-old.
Originally from a Turkish Alevi family, he was brought up by his mother after his parents divorced.
Prosecutors said the boy had shown no remorse for his actions. However, his lawyer said he was cautiously optimistic that the child had understood he had been targeted by propaganda.
A 14-year-old boy has been convicted of terrorism offences in Austria, including a potential plot to bomb a railway station in the capital, Vienna.