Most lumps behind the ear are due to infections or benign tumors of soft tissue origin. Behind the ear there is skin, fat, cartilage, bone, nerves, blood vessels, Lymph nodes, and salivary gland tissue (a portion of the parotid salivary gland extends behind the ear). A bump can develop from any of those structures, and could be due to a tumor (benign or not), an infection (Lymph node or skin), a swollen muscle or salivary gland, etc.
My suggestion would be to wait out for a few weeks to see if it changes in size. If it gets smaller, it was nothing. If it happens to get bigger, then pls get it evaluated from your doctor.An FNAC of the lump will give a clear cut picture.Your father may take some pain killers or some anti-inflammatory drug if pain is there.
Hope it helps.Take care and pls do keep me posted on how your father is doing or if you have any additional doubts.Kind regards.
Thank you for the reply !
I will contact you if the situation change