In general, I'd say Barcelona is not more dangerous than any other big city in Europe. However, Barcelona does have quite a lot of pickpockets. So stay wary of your belongings at all times, especially in crowded and very touristy places. Anyway, in my four years of living in the city (with my blond hair clearly looking like a foreigner), I've never been robbed. Just try not to look too much like a tourist and make sure to follow our Safety in Barcelona Guide.