If you want to avoid the question, you could politely say: 'I'm so sorry, but would you mind if we don't speak about my personal life?' or 'I'm sorry but if you don't mind, I'd prefer not to answer that question'.
However, if you said something like this, it's polite but you would seem a little bit suspicious for not wanting to answer simple questions ;) It might be better to change the subject, or make a light joke of it and say 'Oh, enough about me! I'm not very interesting! What about you? What do you do for living?'