According to NCB officials, Khambatta arrived at the NCB office here for questioning around 10.15 a.m.
An NCB official said that Rakul's summons were issued on Wednesday but she has not yet responded on any available contact so far.
The NCB has also summoned several Bollywood actors, including Deepika Padukone, Shradhha Kapoor, Sara Ali Khan for questioning in a drugs related case.
On Wednesday, besides Deepika, the NCB sent summons to her manager Karishma Prakash for questioning on Friday and Sara and Shradhha for questioning on Saturday.
The NCB registered a case under the NDPS Act on the request of the Enforcement Directorate (ED) probing the money laundering charge into the death of Bollywood actor Sushant Singh Rajput.
The official said that it registered case after few alleged chats of Sushant's girlfriend Rhea Chakraborty, her brother Showik, Sushant's house manager Samuel Miranda discussing drugs came to the fore.
Following the alleged chats, the NCB questioned Rhea, Showik, Sushant's former manager Shruti Modi, talent manager Jaya Saha, Kwan talent management agency CEO Dhruv Chitgopekar, Udta Punjab Producer Madhu Mantena Varna and several others.
Responding to a question on the number of cases the drug law enforcement agency is probing, an NCB official said: "The agency has registered two separate cases under NDPS Act. There are few aspects in both cases which warrant examination of both Sara and Shraddha, so they will be examined in both cases.
The official said that both cases are of NCB and have common link.
The NCB has already arrested Rhea, Showik, Miranda, Sushant's personal staff Dipesh Sawant and 16 others in the case so far.
Rhea, Showik, Miranda and Sawant are currently in judicial custody.
The official said while the alleged chats of Deepika with her manager Prakash discussing drugs in October 2017 has brought her role to the fore, Shradhha and Sara's role came to the fore following the questioning of Saha.
The NCB is the third Central agency to probe the death of Sushant besides the CBI and the ED.