Well, normal is a stretch. It was still forbidden to read and written by a madman in his own blood, driving anyone reading it at least partially insane.
Lovecraft was basing it on The King in Yellow by Robert Chambers. The character itself also appears in the Lovecraft pantheon as Hastur.
I think it being a normal book on the outside is actually scarier. The knowledge in the book was dangerous, not the object itself.
I would never open the Book of the Dead from Evil Dead but I might open the Necronomicon if I find it at an antique bookstore or something.