Of Course! So many times brides worry about having the number of bridesmaids and groomsmen match and they end up stressing about picking more people or less to fit a certain number. But it does not have to be that way! My own personal experience has taught me that it is better to have an uneven wedding party than have people who are not close to you in your wedding or exclude someone who is important to you.
Some of the concerns when having an uneven wedding party can be about what will happen when they walk down the aisle or how will the photographs look, but these are not things to stress about. You can always have all the groomsmen walk after the groom and the bridesmaids walk down the aisle individually or two groomsmen can escort a bridesmaid and visa versa; there are multiple options. Photographs should not be worried about either, having one less bridesmaid or groomsmen will not take away from anything in the pictures.
So if you have three best friends and your fiancé wants four groomsmen, do not worry about finding another person to stand there or make you fiancé choose only three because it is more important to have who you really want, rather than cutting some out or choosing someone to just full in and make photographs balance. The main thing to remember is that you should have the people that mean the most to you standing next to you and supporting you on your big day.