Yes, but be careful.
Flimzy is certainly correct regarding self-answers. Quoting from the help center:
Stack Exchange has always explicitly encouraged users to answer their own questions. If you have a question that you already know the answer to, and you would like to document that knowledge in public so that others (including yourself) can find it later, it's perfectly okay to ask and answer your own question on a Stack Exchange site.
However, I'd caution you to be careful regarding which questions you ask here. Just because it hasn't been asked here doesn't mean that it should be asked here. Stack Exchange's mission is to make the internet a better place, not to answer every conceivable question. That means that if Wikipedia (for example) already contains the answer, asking the question here may not be helpful.
Sometimes easily accessible online sources provide the desired information, but not in a helpful way: perhaps there are no sources, or it's poorly written, or it's only on a random blog. If so, then go ahead and ask here—answers to the question in such cases can easily "make the internet a better place."
So in short, the answer is "yes and no." Don't just ask questions because they haven't been asked yet. But don't let "I already know the answer" be all that keeps you from asking a good question.