This question is quite tricky, you must be thinking that when in an interview you should only provide positive answers but what if the question wants you to talk about the negatives, here the question is asking about the mistake that you made during work and you cannot run away from the question. Answer this question by saying that you made a mistake and you learned from it. Talk about the mistake in detail and then add to it that you will not do the same mistake again as you have learned from it and you moved forward. Do not blame others for your mistake, own it and speak confidently. You don’t have to mention a ‘Critical’ mistake you can speak of a minute mistake as well but be sure to talk about the positive consequences as well.