If you have an attached garage with a door leading directly into the house you should read this fire safety article.
As we understand houses and fire safety more all the time, codes and practices are updated to help make us safer in our homes. Self closing fire doors between the Garage and House, was one of those changes, made to help slow the spread of fire through out the house, allowing you more time to get everyone to safety.
If your home was build before this code was in place, you may not have a self closing fire door, but adding a self closer to the door you do have will keep that door closed in case of a fire.
There are 2 basic options you can install that resolve your issue.
Self Closing Hinges. 
Self closing hinges contain an adjustable spring built into the hinge. If you plan to use these you will need to have a door with 3 hinges and install the self closing hinge where it replaces the middle hinge on your door.
You may want to remove your center hinge and take it to your local hardware store to make sure you get the correct size for your door.
After installation, wind the spring following the instruction that are supplied with the hinge, so the door closes and latches from any position.
Door Closer
A door closer mechanism, attaches to the door and has a closing arm that attaches to the door jamb. They have adjustments to increase and decrease the speed of the closing door. One of the advantages of the door closer over self closing hinges it you get less slam from the door. Also you may not have a middle hinge and don’t have the equipment to install one.
Of course changing the door to a fire rated door is best, but this will help.
