What is a pea sized bump on top of scalp under ths skin not painful?

A pea-sized bump on the scalp that is not painful could be a benign condition such as a sebaceous cyst, which forms when a hair follicle becomes blocked. Other possibilities include lipomas, which are soft, fatty growths, or dermatofibromas, which are small fibrous nodules. While these are generally harmless, it's advisable to consult a healthcare professional for an accurate diagnosis and to rule out any other underlying issues.