"This follows our acceptance of a referral of material from the Electoral Commission," the NCA said.
"While electoral law offenses would not routinely fall within the NCA’s remit, the nature of the necessary inquiries and the potential for offenses to have been committed other than under electoral law lead us to consider an NCA investigation appropriate in this instance."
Banks, who ahead of the 2016 Brexit referendum financed Leave.EU, a campaign led by Nigel Farage, then the leader of the UK Independence Party, has faced questions in parliament about the source of his wealth.
He has repeatedly denied any wrongdoing.