The Keystone NK or Keystone Pup was a two-seat biplane trainer built by Keystone Aircraft for the United States Navy.

The NK was an open-cockpit two-seat biplane with a convertible wheel or float landing gear.

It was powered by a 220 hp (164 kW) Wright R-790 Whirlwind.

The company prototype designated the Pup was entered into a United States Navy design competition for a trainer and was awarded a contract for three prototypes designated XNK-1.

Following evaluation a production batch of 16 was ordered designated NK-1 which were delivered during 1930.