What Causes Flat Brown Bumps On My Penis?

I have a light brown mole at the bottom shady of my penis. I have had this mole for quite some time now. Years. I keep well groomed and have noticed the mole size become larger and it has also grown darker. Upon shaving tonight, it looks like I have discovered 2 more of these same flat light brown moles growing at the top of the base of my shaft. What are causing these moles and should I be concerned?