The ACB had recorded sacked Delhi minister Kapil Mishra's detailed statement last week in the matter and he will be appearing before it again tomorrow.
The anti-graft body had summoned Kejriwal's private secretary Bibhav Kumar last week and he joined the probe today.
"He arrived at 11.30 am at the ACB office. His questioning ended at around 3 pm and he might be called again," said a senior officer.
Mishra had alleged that Kejriwal had influenced the probe into the tanker scam that dates back to Sheila Dikshit's tenure as chief minister.
More From This Section
The sacked minister also claimed that Kejriwal's aide had asked him to delay sending a few reports to the then Lieutenant Governor Najeeb Jung in connection with the alleged scam, sources said.
Mishra had alleged that the investigation into the tanker scam was repeatedly delayed and influenced by Kejriwal and "his two men".
Last year in August, Dikshit was "examined" by the ACB officials in connection with her alleged involvement in the tanker scam besides being handed over a set of 18 written questions.
The Kejriwal-led AAP government had in June 2015 constituted a fact-finding committee to go into alleged irregularities in procuring some 385 stainless steel water tankers by the DJB.
The Delhi government in June 2016 sent a report of the fact-finding committee to Jung following which an FIR was registered in the case.