So I bought 2 different colors of hair color and planned on mixing them. One is a dark brown and the other is medium auburn brown, they are from the same company... I was just wondering if this was OK to do?

Yes, it will turn out a shade in between with an auburn tint. I went to cosmetology school and some of my favorite haircolors I have had were from mixing colors to come up with a new one!

It's okay to mix hair colors, but be sure that they're the same brand. Because some hair coloring products don't contain the same ingredients and if you mix two different brands, it can turn an unpleasant color.