In the case of injury, consult a doctor as needed. Physical therapists may also help to prevent the injury from becoming serious.
If you don't believe it to be serious, try to stretch the surrounding areas. Jay Dicharry of the UVA Speed Clinic recommends Standing Calf Stretches to target the soleus and gastroc muscles of the calf. For a better stretch, roll a towel up like a burrito and place under the big toe of the foot that is in back.
Calf issues, especially tightness, can also be from tight fascia in the foot (plantar fascia). Press the area on the bottom of your foot near your arch until you find a tender spot and/or a tight spot. Continue to apply pressure to that area and flex your toes back and forth for 3 minutes. Repeat on the other foot. That will help to break up any tightness in the foot and achilles, also helping the calf.
Finally, try self massage of the calf area. Run your finger down the bone on the inside of your leg (tibia). Find a sore spot just behind or to the side of the bone. Again apply pressure and this time, flex your ankle back and forth for 3 minutes. This one almost always clears up calf issues for me personally.
If you want more information on Jay, check out the Coach Running Videos.