Is the book of Mormon blasphemy?

I am a devout christian I love Jesus with all of my heart and soul. I keep seeing this Mormon commercials on tv and I just got curious about it and from what I understand the book of Mormon was written by native americans around 400 AD. I mean I'm not trying to be insulting but that just doesn't seem right and I can't wrap my head around how you can just make up your own form of the Bible. Like i said I'm not trying to be insulting I'm just trying to understand so can somebody help me out. Oh and serious Christan and Mormon answers only please I'm not here to start a religious debate with any douche bag atheists...