You'll have to create (subdivide) a new lot to be able to sell it. To do this, the lot will have to be in accordance with your municipal zoning laws - it will have to have sufficient size, access to a roadway (or an easement or right of way through the lot that you're going to keep), water and sewer service (or well and septic) etc. etc. If it meets your zoning requirements, then, sure, you could sell it.
As an alternative, you could sell it to another neighbor who adjoins your lot if he/she would want to annex it onto their lot.