I think so.

When I got pregnant with my DD I ovulated on CD10. I usually ovulate on day 17. I had been charting (as a means of birth control) for many years and I'd never O'd that early. DH and I had unprotected sex because hey - it was only day 10! - and two weeks later I was staring at an unexpectedly positive pregnancy test. I've never ovulated that early again since, it was just a one off.

So yes, it does happen