Yes. The system allows you to ask and answer the question at the same time. There's a check box before you submit your question that lets you answer it at the same time the question gets posted.
Sometimes it makes more sense to have the community answer a question you know to shed a different perspective on it and sometimes it's better to make the answer to your own question especially when you have a deep understanding of the topic and can ask and answer it at your own pace. I've immediately answered questions I've asked the same way, but I've also let the community answer questions that I asked that I hands down could answer.
Remember the goal of this site from the tour of the site:
With your help, we're working together to build a library of detailed answers to every question about music practice, performance, composition, technique, theory, or history.
Long term it doesn't matter if immediately you answer your own question or if you add an answer later or if you never post an answer to it as long as the question and answers help us build up quality content for our site.