The new Assistant Treasurer has made an embarrassing on-air blunder, confusing key budget figures shortly after being caught out snapping a selfie on live television.

Gold Coast Liberal MP Stuart Robert was spruiking the Federal Government's better-than-expected budget figures for last financial year.

"We saw a great result reflecting on the 2017–18 financial year — literally a $19.3 billion turnaround to the lowest debt in 10 years at $10.1 billion," Mr Robert told Sky News.

"Great results."

But it appears Mr Robert has got his debt and deficit confused — something the Opposition swiftly pointed out.

"Somebody needs to tell the poor fellow that that is the deficit number, the $10 billion number," Shadow Finance Minister Jim Chalmers told Sky News.

"Debt is actually at record highs. Gross debt is around $530 billion, the highest it's ever been.

"Net debt is something like $340 billion, which is double what they inherited from Labor."

Shortly before the bungle, Mr Robert had been caught on-air taking a photo of himself in the studio after technical problems meant he could not hear his interviewer.

Mr Robert was a key backer of Scott Morrison's tilt for the leadership and was promoted to the frontbench after the Liberal leadership turmoil.

He had been forced to step down as human services minister in 2016 after questions about his business interests.

An investigation by the secretary of the Prime Minister's department revealed Mr Robert had breached the Statement of Ministerial Standards by having shares in a trust linked to the mining company of a generous Liberal donor.