I am mixed (my father is african american and the teensiest bit native american and my mother is caucasian, mostly of german descent) and i actually never get asked if i am, funny enough!
People assume i'm hispanic and either ask where my family is from and i do get people who don't believe me when i say i'm not. I've even been asked "why would you be ashamed of your heritage?"
It's funny how once some people profile you, you just can't change it!