Malviya, however, tweeted that he had only quoted a news channel.
His tweet came when Chief Election Commissioner O P Rawat was addressing a press conference to announce the schedule for Karnataka polls but had not announced the date.
The BJP IT cell head said the election would be held on May 12 and counting would take place on May 18. While he was correct on the polling day, the votes will be counted on May 15.
When Rawat's attention was drawn towards the tweet, he described it as a "very serious issue".
He said people can conjecture but noted that as information has been "leaked", the Election Commission will probe the matter and take "stringent action" both "legally and administratively".
The CEC later said the tweet was incorrect as the actual date of counting was May 15 and not May 18.
Taking a strong objection, the Congress has dubbed the BJP "Super Election Commission",
Congress communications in-charge Randeep Surjewala also said the Election Commission's credibility was at test and asked if there would be any action against the ruling party and its chief Amit Shah.
"BJP becomes the ‘Super Election Commission' as they announce poll dates for Karnataka even before the EC. Credibility of EC is on test. Will EC now issue notice to BJP President, Amit Shah & register an FIR against BJP IT Head for leaking EC's confidential information?" Surjewala said on Twitter.
EC sets up panel to probe Karnataka poll date leak
The Election Commission on Tuesday evening set up a committee of senior officials to probe the leak of the poll schedule for Karnataka before it was announced by the Chief Election Commissioner earlier.
The committee, which has been asked to submit its report within a week, would also suggest steps needed to prevent any such eventuality in future.
In a statement, the poll watchdog referred to a tweet by Bharatiya Janata Party IT cell chief Amit Malviya in which he had put out the election date minutes before CEC O P Rawat actually announced the schedule at a press conference.
“The Commission immediately directed that the matter be probed and necessary and effective action be taken. Accordingly, Commission has constituted a committee of senior officers of Election Commission to investigate the matter and give its report within seven days.
“The Committee would also suggest steps needed to prevent any such eventuality in future. The Committee set up by the Commission has already sought information from the concerned media organisations and individuals,” the statement read.
In his press conference to announce the poll schedule, Rawat had described the leak as a “very serious” issue that merited a probe and “stringent action”.
'Unfortunately, people believe in WhatsApp forwards'
BJP, Cong accuse each other of hiring firm linked to FB data breach
Congress finally finds its feet on social media
'Not many people talk of the BJP, they talk about Modi'