That's enough to prevent the damage and wear that can release fibers into the air; no sealer is needed. Carpeting and a suitable pad will do the trick. In a basement I'd suggest a rubber-based carpet pad rather than a fiber pad. You could also cover the tiles with new vinyl flooring, linoleum, or even ceramic tiles.
Do you have to remove tile to install carpet?
There is no need to tear out the old tile floor if you want to install carpet. Carpet can easily be installed directly over tile, although you will damage the tile to a certain extent near the edges of the room.