WA Nationals Leader Mia Davies has lodged a formal complaint to the Speaker of the Legislative Assembly over an incident involving Water Minister Dave Kelly.

Nationals MP Vince Catania said he witnessed Mr Kelly "feign a headbutt" towards Ms Davies while she was on her feet speaking in Parliament's Lower House.

Ms Davies did not return calls, but her spokesman confirmed she had lodged a complaint in writing with Speaker Peter Watson.

'While this matter is under consideration she will not be making any further comment," her spokesman said.

Mr Catania said Mr Kelly should apologise to Ms Davies, and if he did not, Premier Mark McGowan should make him.

Dave Kelly described the allegations as "ridiculous". ( ABC News: Irena Ceranic )

"I was very shocked to see the way that that member behaved in such a way, in such an angry manner, towards the Leader of the Nationals," Mr Catania said.

"He feigned a headbutt, it's unparliamentary, he should apologise and apologise to Parliament for his actions."

In a statement, Mr Kelly dismissed the claims.

"The allegations are ridiculous and the official parliamentary footage shows that nothing happened," he said.

WA Premier Mark McGowan said the accusation was nothing more than "politicking on the eve of a by-election".

The seat of disgraced former Labor MP Barry Urban, Darling Range, will go to an election on Saturday.

"I was there, I saw nothing," Mr McGowan said.

"I watched the video, there's nothing. Dave Kelly says nothing occurred and it's Vince Catania who launched the attack.

"It's muck-racking on the eve of a by-election."

Parliamentary vision does not show Mr Kelly making such a gesture, but the footage is inconclusive as he does not appear the frame the whole time.

Mia Davies has lodged a complaint in writing with the Speaker of the Legislative Assembly. ( ABC News: Jacob Kagi )

The incident occurred after Ms Davies had moved a motion calling for Agriculture Minister Alannah MacTiernan's resignation, claiming the sector had lost confidence in the Government and its minister over her handling of live export issues.

Mr Catania immediately tried to make a point of order with the Speaker, alleging Mr Kelly had moved his head towards Ms Davies, but Mr Watson dismissed it.

Ms Davies later made her complaint in writing to Mr Watson.