A member of a royalist group is asking police to take action against a German man who protests against Acting Prime Minister Prawit Wongsuwon and Prayut Chan-o-cha.

Songchai Nienhorm, the founder and leader of the King Protection Group, filed a complaint against Moritz Pfoh in Krabi on Saturday, accusing the 35-year-old German of conducting actions that could incite civil disobedience and interfering in Thai affairs.

Mr Pfoh was in the spotlight on Thursday when media showed him at an intersection in Rayong, holding a photo of Gen Prawit with a large cross mark over the image.

He later told reporters that he was acting to support the "90%" of Thais who did not like Gen Prawit and Gen Prayut, but dared not speak out in public against them.

Mr Pfoh also said he had showed his opposition to Gen Prawit in public on two prior occasions.

Mr Pfoh has been living in Thailand with his Thai wife for eight years.

The wife said her husband was obsessed with Thai politics.

Mr Songchai's complaint was largely based on a report on Matichon online.

"More than 60 million Thais, or about 90% of the total population, were damaged by his groundless claim that they did not favour Gen Prawit and Gen Prayut Chan-ocha," the royalist argued in the complaint submitted to police.

One day after the protest on Thursday, the German and his family decided to leave for Bangkok to stay at a condominium in the capital after police went to his house in Rayong to check his documents and warned him that his visa might not be renewed if he continues his political campaign.