Tamim Khaja​, 18, was arrested on Monday morning when he visited a car park near the Parramatta stadium to meet up with a person he thought was a gun dealer.

In the week prior, he had allegedly scoped out sites including the Parramatta court complex, Garden Island Navy Base and Victoria Barracks. He had also allegedly tried to obtain a semi-automatic firearm.

Fairfax Media has been told that Mr Khaja had included Parramatta courts as a possible target because several other men, some of whom he was close to, had been sent to that court for alleged terrorism offences. He saw it as a way of "getting back" at the authorities for it, one source said.

Among Mr Khaja's close friends are Maywand Osman, who is awaiting trial over an alleged plot to attack government buildings, and Milad Bin Ahmad-Shah Al-Ahmadzai, who has been shooting a man outside a gay swingers club and of threatening to slit the throat of an ASIO officer.

It's understood Mr Khaja had not settled on a specific target and had ruled some out after visiting them.

At a security meeting for District Court staff on Wednesday night, judges and other employees were reminded of safety protocol and security procedures in the event of a terror attack.

Asked if security would be upgraded at NSW courts, a spokesman for the Department of Justice said: "we are continually reviewing and improving security procedures".

"Sheriff's officers have recently been provided with additional training," he said.

"Sheriff's officers work closely with police to address any possible threats against courts. Sheriff's officers also provide assistance to the judiciary, staff and other court users in relation to safety issues."

In September, 40 extra Sheriff's officers were employed as part of the NSW government's counter-terrorism response.

It followed questions put to Attorney-General Gabrielle Upton during budget estimates three weeks earlier that revealed the number of Sheriff's officers had remained largely the same since 2013 despite the changing security environment and increase in court matters.

A review of court security, by the Australian Federal Police and ASIO Protective Security Unit, started in early 2015 and was extended in September due to the increased security alert level.

The review was announced following warnings from local court magistrates that some courts had no security officers on some days.

As well as one charge of planning or preparing a terrorist act, Mr Khaja has been charged with a foreign incursion offence after he was stopped at Sydney Airport on February 27, allegedly attempting to fly to Syria to join Islamic State.

His passport was cancelled, prompting him to turn his attention to a home-grown attack, police allege.

He will return to court on June 8.