Mahmood, who arrived here on Tuesday night on a three-day private visit to India, is scheduled to return to Pakistan with his family on Friday, the sources said.
Mahmood took part in the Eid prayers with his children who study in Delhi.
Mahmood was Pakistan's High Commissioner in India before taking charge as Foreign Secretary in April this year.
He then had said that Pakistan was hoping for "re-engagement" with India after the Lok Sabha polls which were concluded on May 23.
Mahmood had emphasized on "sustained engagements and structured dialogue" as only option to understand mutual concerns and ensure peace, prosperity and security between the two countries.
His visit, even though private, is seen as new initiative from Pakistan to resolve the issues between the regions, but it was not yet clear if he would be meeting political leaders in Delhi.
The Modi government is clear that terror and talks can not go together.
However, an initiative from Pakistan's Prime Minister Imran Khan wishing Prime Minister Narendra Modi on the electoral victory of Bharatiya Janata Party was seen as a positive step for the ties between the two countries which dipped to a new low after a ghastly terror attack in Kashmir's Pulwama in which 40 CRPF personnel were killed on February 14.
In covert operation on February 26, the Indian Air Force (IAF)conducted aerial strikes at a Jaish-e-Mohammad (JeM) terror camp in Balakot in Pakistan. The very next day, IAF and Pakistan Air Force were engaged in an air battle over Line of Control (LoC).
Prime Minister Modi had thanked his Pakistani counterpart for his wishes with a message to him that India always keeps its focus on "peace and development in the region."
But Imran Khan was not invited for the swearing-in ceremony on May 30 which was attended by heads of BIMSTEC countries comprising Bangladesh, Bhutan, Myanmar, Nepal, Sri Lanka and Thailand, mostly SAARC countries other than Pakistan and Afganistan.
( With inputs from IANS )