These types of lumps you found on the back of the neck are quite common. Most of the time they are benign tumors called lipomas or sometimes benign fibromas. These are abnormal growths that do not progress into malignancies, but can be annoying. When they are found they should always be evaluated by a physician to make sure that they are one of these benign growths. In extremely rare cases, they can represent malignant tumors such as a sarcoma. If the lump on the back of your neck is fixed or if it seems to be changing in shape or size, this should prompt you to get it evaluated right away. Lymph nodes that enlarge due to infection or other causes can cause lumps as well, though there really isn't any major lymph nodes in that area. A physician examining the lump will be able to tell you for sure.
I suggest that you schedule an appointment with your primary care physician
. He or she can examine the lump closely, look for signs of other growths in other areas of your body. If your doctor
is at all concerned, then he or she may order some imaging of the area to delineate for sure what it is.