"Are you painting the windows?"
Translation:Fested az ablakokat?
Yes, it's also correct. but the meaning is else:
What are you doing? Are you painting the windows? = Mit csinálsz? Fested az ablakokat? - It emphasizes 'fested'.
What are you painting? Are the windows being painted (by you)? = Mit festesz? Az ablakokat fested? - It emphasizes 'az ablakokat'.