Yes it is.
Your body is in a catatonic state, but isn't dead according to the Magic Jar spell. Note the wording:
The only action you can take is to project your soul up to 100 feet out of the container, either returning to your living body (and ending the spell) or attempting to possess a humanoid's body.
This implies that your body is still alive after casting Magic Jar. While it's alive, it counts as a creature and is therefore a valid target for the Imprisonment spell.
Note that the rules do not give a precise definition of creature, but it would be very strange if a living body were not a creature. Among other things, it would be immune to poison.