Intracardiac thrombosis is a rare manifestation of cardiac involvement in Behçet's disease, and it may be mistaken for a heart tumor. In this letter we present the case of a patient diagnosed with Behçet's disease who was incidentally found to have a mass in the right atrium suspicious of a cardiac tumor. Nevertheless, cardiac magnetic resonance showed a cardiac thrombus. Immunosuppressive therapy and anticoagulation were effective for thrombus resolution.