My Peace lily leaves are turning brown and I don't know why. Could it be that I am over watering it? I am new at this.

If you mean brown tips, some plants are more susceptible than others to get those browning tips,like the Chinese evergreen, peace lily, dracaena, spider and a few more.There can be more than one reason for this happening.
Hard-water use, over fertilizing, over or under-watering, low humidity. wrong light or any combination.
Keep plant on the root-bound side. Water well when the top inch is close to dry, then (empty any excess out of saucer)Keep in indirect light (No direct sun)
Feed moderately, half strength every month or two is fine in the spring/summer months. Use rain or distilled if you think it may be from hard-water. You might always have a few that are brown, but not as many.
If it's the whole leaf browning, you may want to check for small pest.