If the lump is moveable, and feels somewhat soft, it may be a benign (NOT cancer) fatty tumor called a lipoma. They can be removed with a simple procedure, possibly even in the doctor's office with a local anesthetic. If it is more firm, and doesn't move, and seems to be connected to a pore, or if you can squeeze out some white cheesy stuff, then it is most likely a sebaceous cyst, which is something like a giant zit. It too can be removed the same way.
It the lump is hard, or getting bigger, or feels spiky or jagged, then you should see someone about it. Also if it becomes red, painful, or changes color. Come to think of it, given that you are asking the question you must be a little concerned about it. Go and see your doctor. If that doesn't work, ask for a referral to a dermatologist.