They won’t mate in the sense that they’ll get pregnant, but they can tie. Even though it is rare, female dogs can allow male dogs to ride on them even when they are not in heat. Still, it is not common to see this happening. Most female dogs that are not in heat cannot stand having a male dog mount them. They may even fight if the male dog tries to still mount them! Make sure to keep them a distance apart if they show some aggression like this.