Probably just dry skin, but, if the "spot" gets bigger or turns into a lump, I would see a dermatologist.
Please read the information I found online. Don't disregard any spots on your body without first checking with the doctor. Good luck! <3
Benign Brown Spots
The terms "age spots," "liver spots" and "sun spots" share the same meaning and frequently are used interchangeably. These flat, dark spots, like moles, have no significance to the skin or overall health. These benign spots can appear on lips that have a history of overexposure to UV rays. They are permanent, and they can increase in quantity over time.
Pre-Cancerous Brown Spots
Sometimes brown spots in the lips indicate a pre-cancerous condition technically called actinic cheilitis, often referred to as "farmer's lip" or "sailor's lip," which stems from excessive lifetime UV exposure. Most common on the lower lip, individuals with this condition not only have brown spots on the lips, but also complain of dryness and cracking. According to a report on this condition featured on SkinSight.com, actinic cheilitis is more common in older, fair-skinned men, particularly smokers. The same source reports that squamous cell carcinoma skin cancer develops in 6 percent to 10 percent of patients with actinic cheilitis.
Cancerous Brown Spots
Brown spots on the lips can indicate skin cancer. An estimated 3,500 new cases of skin cancer of the lips occur each year, and 90 percent of them are squamous cell carcinoma, according to an April 2008 MSNBC Health report, "Not just lip service: Gloss can invite skin cancer." If diagnosed in its early stages and treated properly, this form of cancer is not as serious as other types, according to the report. But left untreated, this carcinoma can cause lip disfigurement, and in rare cases it can spread and become deadly.
Oral malignant melanoma, though less common, is the more serious form of skin cancer that might first be identified by brown spots on the lips.
Read more: Why Do Lips Develop Brown Spots? | eHow.com http://www.ehow.com/about_5571540_do-lips-develop-brown-spots.html#ixzz1KeP05WQg