Cartoonist Bill Leak says it is "absurd" he has been accused of being racist and that he is being investigated by the Human Rights Commission over a cartoon portraying an Aboriginal father and son.

Leak and The Australian newspaper are being investigated for breaching section 18C of the Racial Discrimination Act after the paper published his cartoon that depicted an Aboriginal man holding a beer can and unable to remember his son's name.

Leak told the ABC's Lateline program that the investigation stifled free speech.

"I think 18C is an abomination. Look, I can only assume that a lot of people genuinely believe that freedom of speech means the legal right to hurl abuse. In fact, nothing could be further from the truth," he said.

"Freedom of speech is what created our civil and free society. It is all about the exchange of ideas, about letting people express their views in the marketplace of ideas."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 6 minutes 58 seconds 6 m Bill Leak speaks to Lateline's Emma Alberici

Leak says he was "bewildered" when he was accused of being racist.

"I have been hammered with this ever since the cartoon was published. But I honestly say to you that when the accusations of racism were directed at me, the only word I can use to express how I felt was just totally bewildered," he said.

"I thought, how could anyone interpret it as racist? A lot of people obviously did. But I can only say what I was thinking when I drew it.

"My concern was for these children and I think right from the get go, even as a child, I think I have always been a very colour-blind person."

Leak's cartoon was in response to the Four Corners report on the treatment of children at the Northern Territory's Don Dale detention centre, many of whom were Indigenous.

"A lot of these kids are coming from the most desperate circumstances," he said.

"I thought to myself, well, it comes back ultimately to parents. We all know that's true.

"But a lot of people would prefer to ... I think a lot of people have got this idea that our Aborigines are sort of safely tucked away in remote communities and let's face it, not many of us city dwellers venture out there and actually see for ourselves what's going on."

Western Australia's top police officer has now spoken out saying Leak's cartoon was an "accurate reflection" of what police officers see in the field every day.

Leak said the saga came after counter-terrorism police advised him to move out of his house because he drew a cartoon featuring an image of the Prophet Mohammed in response to the Charlie Hebdo attacks.

"And now I have been singled out for special treatment by the [Australian Human Rights Commission]. I sort of feel like this is just insane," he said.