The video posted to Facebook also shows an officer kneeling on a protester's neck while two others handcuffed him.
Superintendent Corrie Parnell said police would not comment on individual cases of arrest, and added that images and videos did not provide the full context of what police officers were facing.
"This is an extremely difficult working environment for our frontline staff. However, police have been exercising their powers fairly and professionally, and have used force proportionate and relevant to the circumstances."
A crowd of people getting upset as the protester was arrested could be heard in the video.
"Get off his head," they yelled.
The police officer who was holding the protester's head down released his hold and walked away after another police officer approached him and tapped him on the shoulder.
The Independent Police Conduct Authority general manager Kevin Currie said the organisation had "received several hundred contacts in the form of emails, phone messages and online complaints concerning activities relating to the protest on Parliament grounds and nearby streets".
"We will be applying our normal assessment process to all matters referred to our office. Given the high volume of contacts, our assessment process may take some time.
We will not be providing comment on the content of information provided to the authority at this time," he said.
Yesterday, more than 120 people, including a naked woman who was dragged by her hair, were arrested in a volatile day of "unprecedented" activity.
In footage sent to The New Zealand Herald yesterday, the woman is seen being dragged by two police officers on Parliament's front lawn.
Brett Power, the Taranaki Regional Council candidate who himself was arrested at the protest on Wednesday, says he's spoken to the woman's mother, who described her daughter as "traumatised".
