Depends.
To be street legal, a bike has to be registered. That means that it has to pass an inspection by the relevant authorities. They'll usually require the bike to be fitted with a headlight, a tail/brake light, indicators, mirrors, a speedometer, horn, and of course it all has to work.
Of course the specific requirements may vary from country to country or even from state to state, but the major requirements are fairly universal.
I'm sure your local licensing centre will be able to advise you of what you need to do.