One of the four men accused of the conspiracy to carry out a terrorist attack, in which NSW Police accountant Curtis Cheng was murdered, has reportedly raised his index finger during a court appearance, in a similar gesture used by Islamic State militants.

Milad Atai, 20, appeared in court via video link alongside Mustafa Dirani, 22 and Raban Alou, 18 earlier today.

Mr Atai made the gesture to the camera as the matter concluded in Goulburn Local Court today.

The fourth accused, 23-year-old Talal Alameddine, was the only one to appear in court and to be legally represented.

None of the group applied for bail.

The four men were charged yesterday with conspiracy to prepare and plan for a terrorist attack.

All four were already in police custody over related alleged offences, when the new charges were laid yesterday.

Mr Atai became the fourth person charged in connection to the death of Mr Cheng, who was shot dead outside Parramatta Police Headquarters on October 2 last year.

Mr Atai is accused of helping the sister of the 15-year-old gunman, Farhad Jabar, travel to Syria the day after the shooting.

Jabar was fatally shot by police outside the Parramatta building after Mr Cheng was killed.

Curtis Cheng (left), pictured with his family. (9NEWS)

Police allege the four worked alongside Jabar, and say they have information that they congregated on the day of Mr Cheng’s murder.