You can sprinkle borax around the house as a way to kill fleas, but in my opinion there is a better option, it is best to use a powder like this in conjunction with a flea medication for any pets in your house.
Borax is a wide spectrum insecticide and is effective at killing fleas, but I prefer diatomaceous earth to Borax because it is all natural and non-toxic to animals and humans that come in contact with.
Diatomaceous earth does not contain any pesticides, instead it is a natural powder that is ground from fossils and rocks buried in the earth. It has the ability to kill fleas by penetrating their exoskeletons, yet is totally safe for dogs and cats and any children running around the home area.
The powders are best for killing flea eggs and flea larva that are hidden in the carpeting and furniture of your home. Flea medications such as Frontline is best for controlling the adult flea population, but it can take a month or two for the entire flea population to reach adulthood to be killed by this type of the control. So you might want to combine flea medication for your pets with other products such as flea sprays and powders to speed up the process.