A man on Long Island has been arrested and charged with possessing a knife and wearing a face mask in public, a milestone moment in the debate over whether to criminalize masks in New York State.

The push to ban masks in some public settings began in June after some pro-Palestinian demonstrators covered their faces during protests. They said that they had done so to avoid online harassment, though some activists used the anonymity provided by their masks to harass people or to engage in acts of vandalism.

The man arrested on Sunday, Wesslin Omar Ramirez Castillo, 18, the first to face charges under a mask ban passed this month in Nassau County, N.Y., was not engaged in protest. He was walking down Spindle Road, a residential street of tidy lawns and single-family homes in Hicksville, wearing dark clothes and a ski mask in August, the county police said in a statement.

Christopher Boyle, a spokesman for the Nassau County executive, Bruce Blakeman, a Republican who championed the anti-mask law, said Mr. Castillo “was on the street corner, and somebody called in a suspicious person.”

When police officers arrived, they frisked Mr. Castillo and discovered a 14-inch knife in the waistband of his pants, the department said in a statement on Tuesday. He was charged on Monday with several crimes, including criminal possession of a weapon and a violation of the mask law.

Scott Banks, the chief attorney of the Legal Aid Society of Nassau County, said Legal Aid was representing Mr. Castillo. Mr. Banks declined to comment on the case.