New South Wales principals are being urged to monitor students' actions and consider reporting anti-social behaviour to police amid heightened fears of teenagers becoming involved with terrorist groups.

The Department of Education and Communities issued advice to staff on Thursday "reminding them of the need to exercise vigilance", the department said in a statement.

It said the advice followed a cross-sector meeting earlier this month to discuss the increase in the National Terrorism Public Alert level, which was lifted from medium to high in September.

It also followed news former Condell Park High School student Abdullah Elmir, 17, and a friend travelled to the Middle East to join the Islamic State (IS) movement.

Elmir, whose decision was defended by some of his friends on social media, gained notoriety after appearing in an IS propaganda video threatening western leaders including Prime Minister Tony Abbott.

News Corporation reported his friend, known as Fayez, had since returned to a new school in Sydney to sit his HSC exams after his father tracked him down in Turkey.

The department's advice to staff did not mention the boys, but encouraged principals to report concerns about student behaviour to the department's Safety and Security Directorate, which seconded police to work with incident support officers.

It also said principals could contact NSW Police or CrimeStoppers, or refer to the Secure NSW website for information on the State Government's approach to countering terrorism.