If you are talking about efficiency, this is about 61% (according to Promash) for a standard 5 gallon batch. That's not terribly bad for a typical homebrew all grain system. If you want to improve this, check your grind, make sure the kernels are broken open and that most of the husks are actually shed from the endosperm. The pieces of endosperm should be very small but not to the point of flour. From an efficiency standpoint, the smaller pieces the better, but from a practical standpoint, you still need to be able to sparge smoothly without compacting or sticking. I mill my grain twice with a mill gap of about 0.048". Also check your sparge speed. Shoot for about 1 gallon every 6 minutes. Performing a mashout can also increase efficiency. Grain freshness, how you store it, and even the brand can make a difference too.
If you are talking about from a style standpoint, the BJCP guidelines show an OG of 1.045 to 1.060, so this is fine for an American Brown. You can read more here: http://www.bjcp.org/styles04/.