All electrical appliances have a risk of catching fire and a mini fridge is no exception. This is why you need to take precautions to reduce the risk.
Always plug the appliance directly into an electrical outlet and not to an extension cord or adaptors. There is no reason why you can’t do this with a mini fridge since you can easily place it where there is an outlet.
Be sure that there is plenty of air circulating in the coils and vents to prevent it from overheating. Be sure that the vents and fans are not clogged by dust buildup. Do not put items like cereal boxes on top of the mini fridge. This could also block the heat from escaping.
These practices cannot only pose danger but they make the mini fridge work harder. And if it does, it will consume more electricity.