Ras J. Baraka, the mayor of Newark, accused the Department of Justice on Thursday of selectively prosecuting him nearly a week after federal officials arrested him and charged him with trespassing.

Mr. Baraka, a Democrat running for governor of New Jersey, appeared in federal court for the first time since his arrest on Friday outside a new immigration detention facility in Newark that is expected to play a crucial role in President Trump’s deportation efforts.

The Trump administration has accused Mr. Baraka, who has for weeks protested the opening of the facility, known as Delaney Hall, of barging past its entrance gates and refusing to leave. The mayor has vehemently denied the accusations.

He released video this week that he said showed him being “invited” past the gates before he was arrested, seemingly contradicting the federal government’s narrative that he had entered without permission.

On Thursday, during a brief preliminary hearing in Newark federal court, Mr. Baraka’s lawyers said they intended to file motions to dismiss the case for lack of jurisdiction and for selective prosecution, effectively casting his arrest as politically motivated.

Speaking to a crowd of more than 200 supporters after the hearing, Mr. Baraka described the trespassing charge, a misdemeanor, as a political spectacle orchestrated by the Trump administration that had “humiliated, degraded and demeaned” him.