Yes, you can freeze brown gravy. To freeze, allow the gravy to cool completely, then transfer it to an airtight container or freezer bag. Be sure to leave some room at the top of the container to allow for expansion during freezing. Label the container with the date and contents, and then place it in the freezer. The gravy can be frozen for up to 3 months. To use, thaw the gravy in the fridge overnight and then reheat it on the stove or in the microwave. Note that the texture of the gravy may change slightly after freezing and thawing.