Your refrigerator's temperature control may be set to an incorrect setting. Frost builds up primarily due to the interaction from letting warm air into the fridge freezer. To avoid this, try not to open the door too often, and don't leave the doors open for very long.
If vents are blocked, airflow will decrease. Temperature and moisture issues may arise due to blocked vents. Items placed directly in the air flow from the freezer compartment to the refrigerator compartment may freeze. Do not place temperature sensitive items, such as eggs and liquids, in these areas.