they might be tense, if not from exercise. Do you sit around too long? keeping your legs in one position for long periods can cause muscle pain. Try stretching your calve muscles 3 times a day for at least 15 secs.
"It sounds like to me you definitely had a "charley horse" in your calf muscle most likely caused by exercising and being dehydrated. Those hurt so very bad and the pain and soreness can last for a few days afterwards."