Possibilities... If you are coughing the mucous, you may have chronic bronchitis, a form of copd. You will need a doctor evaluation and possibly pulmonary function tests to verify this diagnosis. There are treatments to control symptoms but no cure. If you are smoking, you need to quit to slow disease progression and control symptoms.
Probably not normal. It could be allergies, or it could be a sign of infection or asthma. Typically the mucous either drains from the nasal passage/sinuses down into the throat, or the mucous comes directly from the lungs themselves. An allergist or lung specialist can help you make the diagnosis and treat you.