At this time a Brainshark Curriculum cannot be made directly inactive. Curriculums act like a thread that ties courses together in a particular order, and allows enrolled users to be brought from one course to the next once using one single enrollment.
As an alternative, you are able to delete a curriculum from your Brainshark Learning page. Deleting a curriculum will remove all current enrollments from the curriculum, but will not delete any of the courses that make up that curriculum. Each of a curriculum's courses would need to be either inactivated or deleted individually if you wish to make these inaccessible as well.