You can read about crime in the manual.
You can check your current crime level on your character's info screen (under health and mana). If it's more than 0 and you get near guards they'll try and arrest you. You need to pay a fine or go to jail for a time. (Or, you can find "other" ways to get rid of your notoriety but as you don't seem to choose the life of crime, I recommend either paying the fine or reloading an earlier save where your crime level is 0.)