The Board is also investigating the assets of some other members of the Pakistan team including captain Misbah-ul-Haq and former Test opener Imran Nazir.
"The assets of Butt are again being looked into after some of the evidence was examined at the spot-fixing trial in London," one source said.
The source said Butt's assets came under scrutiny after it was reported during the trial that he had moved an amount of around USD 181,000 from a bank account in Lahore to his mother's account last year in September when the spot-fixing scandal first broke out.
He said the assets, including cash and movable and immovable properties belonging to Asif and Aamir, were also being scrutinised and efforts were being made to confirm their sources of revenue.
Another source said as far as Misbah was concerned the Board believed he was a defaulter of income tax of around Rs 3.7 million while Nazir had also not paid taxes amounting to Rs 1.1 million.
But a source close to Misbah said that the whole issue was a misunderstanding as most of the taxable income of the players was deducted directly by the Pakistan Cricket Board.
"Apparently there is some confusion over what exemptions on wealth and property are allowed to the contracted cricketers of the board and former Chairman Ijaz Butt had been vigorously been pursuing this issue with the government before he stepped down," the source said.
The source said three of the players under investigation have already been issued recovery notices on account of defaulting on their tax payments.