The two men — one of whom is a 26-year-old Austrian of Afghan origin – were arrested on Friday, a spokeswoman for the prosecutors' office told AFP.
She declined to reveal the nationality of the other suspect.
A request would be made later on Sunday for them to be held until trial, the spokeswoman added.
Last month, an Islamic State supporter who had been convicted and imprisoned for trying to join the IS group in Syria went on a shooting rampage in central Vienna, killing four people, aged between 21 and 44.
The 20-year-old gunman, a dual Austrian-Macedonian national, was shot dead by police.
Eighteen people have since been detained in Austria and Switzerland in connection with the attack and the government also ordered the closure of two mosques in Vienna frequented by the attacker.
Until the deadly shooting, the country of 8.9 million people had in recent decades been spared the shock and mayhem wreaked by major terrorist attacks.