Depends.

If you read her body language correctly, then an out of the blue kiss can be quite a turn on. Before I got with one of my ex's we were flirting, and he just leaned in and kissed me right after saying something dirty. I wasn't complaining in the least and we ended up going out.

But if you read her body language incorrectly you're setting yourself up for a very embarassing situation. There's no harm in asking whether it would be cool to kiss her, provided you do it in the right way. Stuttering and stammering is probably not the way to go, unless she like the cute&shy type. Another ex of mine, again before we were going out, was telling me how much he liked me, and that he'd really like to spend more time with me and finished off this really long speech with "but can't I just kiss you now?" and that worked as well.

Good luck either way!