Police in Medicine Hat say they started an investigation on Boxing Day into comments posted on Facebook.
Investigators say the post included remarks about the deadly shooting in Newtown, Conn., and a threat aimed at a Medicine Hat school.
Police did not go into detail in a news release issued Friday evening, but did call the post "disturbing."
The 18-year-old was arrested and has been charged with making threats and publishing obscene matter.
He is being held in custody until his next court appearance Monday.
Police have not named the man charged or the school involved. They also didn't say whether he was a student at the school.
It's the second time in the space of a little more than a week that a young person has been charged with making threats aimed at an Alberta school.
On Dec. 21, a 17-year-old student at Ponoka Composite High School, south of Edmonton, was charged with making threats.
Area schools were put in lockdown while the boy was arrested at his home. Police say they seized two rifles and ammunition.
The youth was released on bail Friday.
There was rash of threat-related class cancellation and school closures in Alberta on the same day as the Ponoka arrest.
One of those school closures came in Medicine Hat.
Classes were cancelled as a precautionary measure at Crescent Heights High School because one student overheard another student talking about school violence.
School officials termed it a "low risk issue."
— With files from CJCY in Medicine Hat.
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