The incident occurred with 4:19 remaining in the second quarter of the Nets' 114-107 loss to the Cleveland Cavaliers on Monday.
A fan courtside could be heard heckling Irving, who responded with obscene language.
Irving has appeared in five games for the Nets this season, averaging 22 points and 5.4 assists. He scored 30 points in 38 minutes during a 119-118 win over the Washington Wizards on Wednesday night.
Irving is unvaccinated against COVID-19, meaning he can't play in home games due to a mandate in New York City. After Irving was away from the team for almost three months, the Nets reversed course last month to allow him to participate in road games.
Wednesday marked the two-week anniversary of his return.