Is it safe to exhaust a portable electric clothes dryer indoors?
Portable probably means electric, so yes that should be safe in the short term.

You may soon have mold problems and the like from excess moisture, if you keep doing this, but there's no immediate danger from the exhaust, as would be the case with a gas dryer which exhausts combustion products.

You could simply put clothes on hangers and set them to dry - during the winter, they dry fairly quickly just hanging on the shower curtain rod over the tub, without blowing lint around the house.