It's usually best freshly made however YES it can be frozen. After it has been cooked allow it to cool. Wrap well with a few layers of plastic wrap followed by an outer wrap of foil. Freeze for 2-3 months.  To thaw: place in the refrigerator for 12-24 hours. When thawed reheat in the oven or microwave. NOTE: the ingredients used in the frittata can affect it's texture after freezing and thawing.