Mustappa bin Haji Sirat (born 4 October 1957) is a diplomat and politician in the Government of Brunei.

[3] In November 1982, Mustappa started working in the Ministry of Foreign Affairs as the director general in the Association of Southeast Asian Nations (ASEAN)–Brunei division and later the Policy Planning Department.

[6] He met with Ashton B. Carter to discuss future collaborations between the two nations in Washington, United States on 27 June 2013.

[10][11] China ambassador to Brunei visited Mustappa and congratulated him on his newly appointed position, followed by discussions focusing on improving transportation and communication between the two nations on 18 November.

[14] He participated in the Fadhil Yunus & Adib Noor The BMW Golf Cup Brunei 2021 on 17 September 2022.