Anyone visitor, worker or student from a foreign country visiting the United States can use their home country driving license legally on US roads for up to a year. The only condition is that the home country must have ratified The 1949 Geneva Convention on Road Traffic. Kenya is one such country.
You can therefore use your Kenyan driving license to drive on US roads for the first 12 months following your date of entry (as stamped on your passport). After that you have to apply for a US driving license at your resident State Motor Vehicle Division or Department of Motor Vehicles (DMV).
Also, note that you can only drive the vehicle categories endorsed on your Kenyan driving license. Thus, if your license only allows you to drive a small car, you cannot drive a bus or truck.