This is Nadir Baba Türbesi. From a site I gather: "

The tomb is 50 m east of Arap Baba Masjid. This tomb consists of two parts. The first section after the outer door is the mosque section, and the office section is reached from here. The grave part is covered with a wooden sarcophagus. Nadir Baba is a person who lived in the Seljuk period. It is highly probable that he is a sheikh belonging to the Yesevi order. As a tradition from the past, in the early 1900s, religious circles in Harput and people of the sect frequently gathered here (see Türbeler / Tayyar Baba) to have conversations."