“This is travesty of justice,” said Muhammad Shoaib Shaheen, another lawyer for Khan, on Tuesday.
Wednesday’s hearing was held under the colonial-era Official Secrets Act, with only lawyers present.
According to a report by the government’s Federal Investigation Agency, the case relates to a cable that Khan presented as evidence that he was ousted as part of a US conspiracy backed by the establishment.
The United States and the Pakistani military have denied the claim.
Former foreign minister Shah Mahmood Qureshi, vice-chairman of Khan’s Pakistan Tehreek-e-Insaf (PTI) party, has also been arrested in the same case.