Is it possible my computer is listening to my conversations?

I've come to accept the fact that my computer reads my emails, and the ads that pop up on websites I look at are strategically placed accordingly.  But, now I'm worried it's spying on me on a whole other level that I'm pretty sure isn't even possible.

A little while back I had a conversation about a weird restaurant/theater called Medieval Manor that I walk by on my way to work.  The next day, an ad for that very place appeared.  It was a strange coincidence, but I was able to write it off as just that.

This week I was again having a conversation (not through my computer via Skype or Gchat or anything like that, just out loud in its general vicinity while it was on), this time about a new flavor of Oreos--S'mores.

That same night, an ad for s'mores appeared on a website I was viewing.  Should I be scared?

Follow @LucidSportsFan