When such a great and exalted personality as the Lord behaves like an ordinary human being although possessing inconceivable qualities, His behavior is called māyā. Therefore the Lord is described as māyā-manuṣya. This is the opinion of Śrīla Jīva Gosvāmī. Mu refers to mukti, or salvation, and ku refers to that which is bad or very obnoxious. Thus muku refers to the Supreme Personality of Godhead, who saves one from the bad condition of material existence. The Lord is called mukunda because He not only saves the devotee from material existence but offers him transcendental bliss in love and service.
As for Keśava, ka means Brahmā, and īśa means Lord Śiva. The Personality of Godhead captivates both Lord Brahmā and Lord Mahādeva, or Śiva, by His transcendental qualities. Therefore He is called Keśava. This opinion is given by Sanātana Gosvāmī in his Vaiṣṇava-toṣaṇī commentary.