It did not happen to me but it was mentioned in some pregnancy books I read as a perfectly normal thing when it happens, not a sign that you're going to deliver soon. But make sure to mention it to your Obgyn of course.
I have heard other women describe this, although it wasn't my personal experience. Mind you this was my first pregnancy, so I'm not certain I could have identified sensations like that, know what I mean? I doubt this is your body thinking it's time as I have never heard of this being linked to premature labor or anything, but as always, when in doubt, give your Dr. a call. I suspect this is pretty normal though. Hope your doing well!!