Is copying an image from a previous paper of mine and citing its source considered self-plagiarism or unprofessional?
There is such a thing as self-plagiarism, but I would say that your case (reusing a figure that you created and providing a citation to it) is not an instance of it.  I also don't think it is unethical or unprofessional.  As Ran G. says in his answer, just make sure you ask permission from the copyright holder (if it isn't you).