A teenager accused of being involved in a plot to target Anzac Day commemorations who had terror-related charges against him dropped has walked away from court without a conviction for weapons-related offences.

Huran Causevic pleaded guilty in August to three weapons offences, including possessing an AK-47 knife that police found under his bed.

The 18-year-old, from Hampton Park in Melbourne's outer south-east, was also charged for illegally possessing knuckle dusters, while another knife was found in a car.

Magistrate Jelena Popovic handed Mr Causevic a good behaviour bond on the condition that he continue to have psychological treatment.

Terrorism-related charges levelled against the teenager were dropped earlier this year after he had been accused of being part of a plot to launch an attack at Anzac Day commemorations in Melbourne.

He had been in custody for five months until prosecutors withdrew the charges.

Causevic was the first Victorian to be held under a preventative detention order (PDO) when he was detained without charge following counter-terrorism raids related to the alleged plot in April.

Judge Popovic told the court she could have made a ruling on the weapons offences at the time the terror charges were dropped.

But she said she wanted an adjournment to ensure that he attended the psychologist, and told the court she was pleased he had made gains in his treatment.

"I apologise to the family for dragging this out," she said.

She said she hoped this would help counteract the effects of post-traumatic stress related to his 129 days in incarceration.

Victoria Police had used the PDO to hold Causevic, because of his alleged close association with terrorism suspect Sevdet Besim, and Numan Haider.

Haider was shot dead after attacking police with a knife at a suburban police station in 2014.

Besim is in custody after he was charged with conspiring to commit a terrorist act and was denied bail.

A third man, Mehran Azami, was not charged with terrorism-related offences, but charged with importing weapons from a Chinese weapons importer.