When i turn my 2006 mustang on it shows that my overdrive is on. is it supposed to be on everytime i start my?

saying that u have an overdrive gear u have an automatic and yes it can be on every time u start the car u shood have a on on your gear shifter that will turn it off but u only need to do that if u are wanting to stay in a lower gear 4th gear to be exact overdrive just gives your transmission a 5th gear to go in when at a low rpm