At noon on Tuesday, the benchmark S&P/ASX200 index was down 1.9 points, or 0.03 per cent, to 7018.7. The broader All Ordinaries was up 8.9 points, or 0.12 per cent, to 7268.4.
The ASX's 11 official sectors were mixed, with four losing ground and seven gaining it.
The biggest mover was financials, which had fallen 0.95 per cent after NAB warned full-year costs were expected to grow by three to four per cent.
Australia's second-biggest lender cited a $60 million to $100 million top-up to payroll and customer remediation charges for existing matters, as well as higher personnel and leave costs.
NAB shares were down 3.4 per cent to $29.66, putting the bank on track for its worst day since June 14.
Among the other big banks, CBA was down 1.4 per cent, Westpac retreated 1.3 per cent and ANZ dropped 0.7 per cent.
The heavyweight mining sector was up 0.7 per cent even as BHP was down 0.1 per cent at $39.08. Fortescue had risen 1.1 per cent to $19.17 and Rio Tinto was up 0.2 per cent to $99.80.
Potential takeover target OZ Minerals had retained Monday's 36 per cent rise and then some, rising 0.7 per cent to $25.76.
Megaport was up 8.4 per cent to $8.87 after the Brisbane cloud computing company announced its full-year global revenue had risen 40 per cent to $109.7 million, compared to a year ago.
REA Group was up 3.5 per cent to $128.385 after the realestate.com.au owner announced full-year net profit after tax had risen 25 per cent to $408 million.