Should I tell the men that I've just started dating, that I'm dating other people as well?

I’ve just started dating, as in online dating, and I’ve got several people I’m meeting. If I’m busy on a certain night that someone asks me out, should I confess to having another date planned with someone else, or should I just say, I have plans and then, if pressed, make up some thing more benign. On the other hand, maybe it’s healthy for the guys to know there’s some competition.