One can keep freshly baked brownies up to four day at room temperature in a closed plastic container. However, this is only true for brownies that do not have a frosting that consists of eggs or dairy ingredients such as buttercream.
To keep brownies moist on a counter top, one also can place a bread slice in the plastic container before closing it.
Cooled brownies can be frozen and kept for four to six months. Before storing in the freezer, one can wrap them in plastic wrap or aluminum foil and place them in an air-tight freezer container. If brownies need to be stacked in the container, wax paper sheets can be placed between each layer.