Hmmm...
Maybe you are starting to think about a new level of seriousness in your relationship, taking it a step further (not neccessarily marriage), but you have a fear that your girl doesn't want anything more serious. You know you have the ability to get the ring out, but you are scared that she won't be as ready for commitment as you.
I don't really know you or her, so thats an uber vague stab in the dark, but there you go. My recommendation would be to mention it to her in passing (the dream, that is) and see what she thinks about it. Again, its up to you how you interpret it, as it is your life, who knows it better?