Stress, poor posture, using poor lighting when reading or working and vigorous gum chewing can cause a stiff neck and headache to occur simultaneously, according to Everyday Health. More serious causes include migraine headaches, temporomandibular joint disorders, meningitis and injury to the head or neck.
Temporomandibular joint disorders result from improper jaw alignment or excessive clenching of the jaw. Meningitis is a serious, sometimes fatal infection of the tissue that surrounds the brain and presents with fever, neck pain and headache, according to Everyday Health.
While tension is the most common cause of headaches accompanied by neck pain, it is important to seek medical assistance if the pain is severe, fever is present and the patient is sensitive to light, as these symptoms may be signs of a more serious condition.