Aortic mural thrombi of the ascending aorta are rare. If an aortic mural thrombus is dislodged, it can cause various embolic complications, which can sometimes be fatal. Although contrast-enhanced computed tomography (CT) and transesophageal echography are useful for diagnosing aortic mural thrombi, four-dimensional CT (4D-CT) is one of the most useful modalities for both diagnosis and treatment selection in such cases. 4D-CT can be used to evaluate the morphology and mobility of thrombi. Furthermore, it is minimally invasive. To the best of our knowledge, there have not been any reports about 4D-CT being used to depict an asymptomatic ascending aortic thrombus. We report a very unusual case, involving an aortic mural thrombus of the ascending aorta.