Biceps brachii is a muscle belonging to the flexor compartment of the arm. It has been described as one of the muscles with most frequent anatomic variations. The objective of this study was to determine the prevalence of third head of the biceps brachii muscle. A total of 14 cadavers of both sexes (13 men and 1 women) with different age group were used for the study in the Morphology Laboratory at the University of Pamplona. On the right side the origin of extra head biceps brachii muscle was given bicipital groove level in relation to the distal portion of the pectoralis major muscle, the distal insertion was joining with the short head of the biceps brachii. In the left arm of the second body, extra head biceps brachii muscle originated from the anterolateral surface of the humerus between coracobrachialis muscle insertion and origin of brachialis muscle; its distal insertion occurred in the long head of biceps brachii muscle. The dual origin of the third head of the biceps might contribute to supination of forearm, as the muscle origin appeared in a lateral position relative to the rotational axis of the arm. The knowledge of such anatomical variations is important for anatomists in the academic study and clinicians in order to avoid errors in the diagnosis or undesirable consequences during surgery, procedures safer and more efficient rehabilitation.