If our attorney is also representing an investor, does this represent a conflict of interest?

The situation you have mentioned may certainly represent a conflict of interest that you should minimize or even avoid altogether. Though it would seem that both your investor and your company are working toward the same goals, how you reach those goals and who it favors more along the way may become a point of conflict. Having the same attorney represent both sides of that business venture may potentially prove problematic.

For example, the investor may direct the attorney to draft terms for the investment that, at first, may seem favorable to everyone involved. However, after a few years of business, the investor may end up with the better end of deal that you are stuck with due to the attorney not looking out for your interests 100%.

Ideally, you should avoid using the same attorney for this investment altogether. If that is not desirable to or feasible for you and you wish to continue using this attorney, I would suggest the following: (1) make sure the attorney and the investor acknowledge the potential conflict of interest and preferably put this in writing; and (2) if possible, once terms are proposed, seek the opinion of an independent attorney to ensure there are no terms that may prove unfavorable for you down the road.