An Adelaide man who downloaded a video of the Christchurch mosque attack "out of curiosity" has been spared a conviction because it could harm his prospects of employment.

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Justin Robert Bassett, 28, pleaded guilty to possessing extremist material in the Adelaide Magistrates Court today.

The court heard the father-of-one downloaded the video two weeks after the massacre in March 2019, but had last viewed the video in April this year, prompting police to search his property.

Police seized Bassett's computer and hard drives which contained the extremist material and arrested him at his Surrey Downs home.

The court heard Bassett claimed he had not actually viewed the video recently but may have opened it as he went through the computer folder.

Bassett's lawyer Jason Evitts told the court his client did not have any reasonable excuse to possess the material but had downloaded it as a "matter of curiosity".

"He's realised the enormity of having access to this material and possessing it," he said.

"This man accepts the video circulated had disturbing content.

"He fully accepts responsibility for his actions.

"He's deeply embarrassed by it."

Evitts asked Magistrate Simon Smart to spare his client a conviction because it may harm his employment prospects as an apprentice bricklayer.

Bassett provided a letter of apology to the court and a number of character references describing him as "a good member of society" who "does not advocate for this sort of stuff".

The court heard he had no criminal history.

Magistrate Smart fined Bassett $1250 plus police and court costs but spared him a conviction.

"You've done a foolish thing and that foolish thing was a criminal thing," he said.

"You can understand how it would be a matter of great distress for the relatives of the people killed and members of the public, wherever they may be, would have a problem with such material.

"Clearly you succumbed to the temptation to view material in a foolish and ill-considered act."

Magistrate Smart said he was satisfied that Bassett had matured since his offending and was unlikely to reoffend.

The charge of possessing extremist material carries a maximum penalty of two years imprisonment or a fine of up to $10,000.