The 19-year-old was at Newcastle MP Tim Crakanthorp's office about 12.30pm on Wednesday before authorities received a welfare report about his behaviour.
Police went to the office and found the weaponry.
Investigators confirmed the man circulated a manifesto to a number of media outlets and public figures.
Mr Crakanthorp, who did not indicate if he was in the office at the time of the incident, said no one had been hurt.
"I have been advised that the individual briefly walked in and out of my office, he left before making any contact with my staff," he said.
"I have spoken with police and they are managing the situation and have assured me that nobody was harmed."
The man has been charged with preparing or planning for a terrorist act.
He was taken to the Newcastle police station and is co-operating with investigators.
The teenager is due to face Newcastle Local Court on Thursday after being refused bail.
There was no ongoing threat to the public and a Joint Counter Terrorism Team was continuing to investigate the incident, police said.
It came on the same day Premier Chris Minns joined Mr Crakanthorp in Newcastle for media events, including the inspection of a soon-to-open walking and cycling track.
They were joined by Counter-Terrorism Minister Yasmin Catley.
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