"Why was Trivedi arrested and cases filed against him? Those who committed treason are free and one who just drew a cartoon was jailed," Raj Thackeray told reporters in Mumbai on Tuesday evening.
"Afzal Guru and Kasab have not been hanged yet. Is this not a mockery?" Mr Raj said.
Defending Mr Trivedi, Mr Raj, himself an able cartoonist, said, "What wrong has he done? He was merely commenting on corrupt politicians.
"What is wrong in expressing anger through cartoons? One should understand the motive behind the cartoons," he said.
"When I saw those cartoons, I thought what was wrong with them. I don't think there is anything wrong with his cartoons."
The MNS chief reiterated that Home Minister R R Patil was incapable of handling his ministry. "R R Patil doesn't understand the home department. How can he be expected to understand cartoons," he said.
Raj Thackeray recalled that his uncle, Shiv Sena chief Bal Thackeray, had given him his first lessons in the art of cartoon-drawing.
Mr Trivedi was arrested on Saturday for cartoons which depict the national emblem and the Parliament in allegedly objectionable manner.
Earlier this evening, Bombay High Court granted him bail, in response to a PIL.