Yep. Running (or other moderate exercise) doesn't seem to have any effect on the quantity or quality of breast milk. Just remember to take care of your breasts by wearing a supportive, well-fitting bra and breastfeeding baby before heading out for a run (breasts that have been emptied of milk are much comfier for running). Be sure to stay well hydrated too, and keep an eye on your weight: If you start losing more than a pound each week, you probably need to add more (nutritious) calories to your diet.
Note: Always get an okay from your doctor before starting an exercise routine postpartum.