Steelers safety Kameron Kelly was arrested Friday ... after he allegedly made "terroristic threats" during an altercation at a Pittsburgh-area bar.
According to court documents obtained by KDKA, cops were called to Mario’s South Side Saloon after 23-year-old Kelly refused to leave the pub.
Police say Kelly was combative, and after they instructed him to leave the bar area ... he refused -- and still tried to make his way back in.
Cops also say Kelly had threatened a male bar staffer ... saying he would "knock out" the man.