Yes, it's designed for that. The charger has maintenance mode.
When the red light remains on continuously, the pack is fully charged. It can be used then or left in the charger. The charger will maintain the charge without overcharging it. For long-term storage, it's actually a good practice to store it in the charger in a cool, dry place.
HEADS UP: Always follow the correct charging procedure. Plug the charger into the outlet before inserting the battery pack. And remember, these chargers are only for charging DeWalt rechargeable batteries. Any other use risks fire or electric shock.