To be honest, I wasn’t totally sure either, so I tried it.
Yes, you can reblog one of your own posts on the same blog. (Though I’m not sure why anyone would want to do this unless they wanted to experience Inception.)
The easiest way to do this is to go to your blog and click the ‘Follow’ button in the admin bar at the top of the page. You’ll now be following your own blog in the WordPress.com Reader. From the Reader, pick a post that you want to reblog, then follow the instructions here to reblog the post.