A teenage boy who was radicalized by Islamic extremism content online has pleaded guilty to preparing for a terror attack in Sydney.

The 16-year-old boy, who has not been identified, pleaded guilty to committing acts in preparation for a terror attack during a hearing in the New South Wales Supreme Court on Tuesday.

The court heard that the boy was first exposed to extremist material online in 2024 before he began communicating with others about Islamic extremism and conducting online research into targets and methodologies for an attack involving explosive devices.

The court was told that the boy spoke to other people online about potential attack sites, including the Sydney Opera House and Sydney Marathon, but that he never took any steps to obtain materials required to make a bomb.

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"I am picking the location, places where lots of people and tourists are out," he said to someone online.

He was arrested at his western Sydney home in August 2024, where federal police officers found more than 40 videos containing extremist content on a computer.

He will be sentenced by the Supreme Court in October.