Sanders won with 84 votes, while former Vice President Joe Biden received 48 votes and two went uncommitted. Sanders' win in the contest translates to four national delegates, while Biden captured two.
The Northern Mariana Islands, which has been a US territory since 1975, participates in the presidential primary process but not the general election. In 2016, Hillary Clinton won the Democratic caucuses while Donald Trump won the Republican caucuses.
Biden has a near 150-delegate lead over Sanders, after the former vice president racked up a series of victories earlier this month that catapulted him to front-runner status, according to CNN's delegate count.
Sanders on Wednesday vowed to stay in the race despite the narrowing path for him to win the nomination.
The two candidates are scheduled to debate Sunday, which has been moved from Arizona to Washington, DC, amid coronavirus concerns.
The debate comes ahead of another round of Democratic primaries Tuesday in Arizona, Florida, Illinois and Ohio, which total to 577 delegates up for grabs.
This story has been updated with additional background information.
CNN's Veronica Stracqualursi contributed to this report.