It's not only safe, but a beautiful country to visit. Don't just go to the capital and live in the urban.
Go in the mountains "Rila" "Pirin" I thing "Stara Planina" was the longest one on the Balkans, visit the old castles in northern Bulgaria "Belogradchik rocks" "Baba Vida castle" and absolutely amazing nature. "Carevec castle" placed in Veliko Tarnovo I can write whole day.
Oh, I forgot "Black Sea" and the beautiful towns on the coast. Strongly recommend "Nesebar".
And to answer your question.
I think it's safe if you are doing good and not looking for trouble, then everything's gonna be fine. :)
Travel safe.