The nearest airport is Boston Logan International Airport (BOS), which serves numerous domestic and international flights.
BOS is ~7 miles from the Northeastern campus: https://goo.gl/maps/mJvsL2KRg5U2.
To travel to/from the airport to campus or your hotel, you can take the MBTA (~40min by bus/subway) or taxi/Uber/Lyft (~15-30 min by car).
The Logan Express bus also provides transportation to/from BOS airport. The Back Bay stop of the Logan Express is convenient for those staying at downtown hotels: http://www.massport.com/logan-airport/to-from-logan/transportation-options/logan-express/back-bay/