We report a rare case of an extramedullary plasmacytoma (EMP) in the frontal sinus with an indolent clinical presentation. Although a history of trauma was absent, the initial diagnosis was a mucocele, based on the radiological findings. Upon surgical excision, the patient was found to have an EMP. EMP, a form of solitary plasmacytoma, has a significantly high rate of conversion to multiple myeloma. This mandates long-term follow-up, even after successful radiotherapy and/or resection. While radiation therapy is generally considered a first line treatment for EMP, surgical intervention may provide optimal treatment in complicated cases. This case presentation highlights the prognosis of patients diagnosed with EMP.