Should I explain my criminal history to my potential new employer?

I have been hired through a temp agency to work for an insurance company. I really want to be hired on permanently. The temp agency informed me that the company had ordered my background report. I have a xanax possession charge that was dropped and 3 counts of use or possession of paraphernalia. I was not convicted of anything. I entered a pre-trial diversion program, and for the paraphernalia charge, prosecution was terminated. This was 4 years ago, and I have no drug or legal problems at all. I just want to know if I should address it right off since I know they will see it. Once they see it, I don't know if I'll have the chance to talk about it.