A 15-year-old Sydney boy accused of conspiring to prepare for an act of terrorism has been released on bail.

The teenager, who was arrested in counter-terrorism raids last December, is among five people accused of plotting to target government buildings, including the AFP building in Sydney.

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The boy faced a Supreme Court bail hearing by video link, supported by up to a dozen family members who watched on in court.

Referring to the allegations, Justice Michael Adams said people who hold extremist views and a willingness to kill or injure were “very dangerous”.

Justice Adams said he suspected the teen was influenced by his older co-accused.

He said some of the evidence revealed “a degree of empty, or at least aspirational bravado” on the part of the accused.

The court also heard the youth was suffering a psychological illness that could worsen if he remained in custody.

Justice Adams described the case as exceptional.

“His relative youth and his psychological condition make it exceptional,” he said.

The teenager, who cannot be identified because of his age, was ordered to live at a specific address, to report to police daily and has been banned from using a mobile phone or the internet.

-ABC