By formal definition, field mice are the same species (Mus musculus) as house mice. They are a non-native species, introduced from India, and are in a different taxonomic family from any of the native mice. For more information on our tiny furry friends, see the mice entry.
Any time a new development gets built on land that was previously farm land the previous residents will attempt to take up new living space. If you live in a recently built house chances are good that you'll have a higher rate of these visitors for the first few years. As local wildlife they are part of the food chain for snakes and owls among others.
Note: Mice are achingly timid and have a high metabolism. Wild mice can die of terror, suffering cardiac arrest, simply by being cornered and picked up. Please be gentle if you are dealing with a wild mouse and humane if you are dispatching one.