Praise be to Allah.
Yes, it is permissible to pray with one’s head uncovered, but it is better to cover it, because that is more decent. One should also cover one's shoulders, according to the madhhab of Imaam Ahmad, because the Prophet (peace and blessings of Allaah be upon him) said: “No one of you should pray in a single garment with nothing of it covering his shoulders.” (Narrated by al-Bukhaari, 1/498; Muslim, no. 516).
