http://i.imgur.com/IOzgDf1.jpg
It's probably because you're a foreigner and they don't get many of those there. Relax, they're only curious.
It is impolite to stare at unknown people, so, any adult in clear mind would try to avoid doing it.
If you look like person on the picture, I might have explanation. Try to shave every day. With beard you might look like potential terrorist. People are just being cautious.
Another explanation is you just look as 99,99% foreigner. "Southern European"/"Latin American" appearance is pretty rare in Russia. People just trying to guess if you fall into 99,99 or 0,01% category.
Shave in the morning and you will figure out it immediately.
Привыкай.
if you don't speak russian and you go to small places that they are not touris destination they are just curios, russian are frendly people they probably just want to meet you :D be nice :D
You have that uncanny valley look.
not how you look, but how you ACT will draw stares.