A group of territorial defence, or Ror Dor, students said people who have no gratitude toward their motherland and His Majesty the King should leave Thailand, according to army chief Apirat Kongsompong.
The army chief shared the students' thoughts after he met 62 of the students from 19 different high schools in Bangkok and neighbouring provinces.
Gen Apirat said those are "their words".
Thai tradition is rooted in a strong relationship between the monarch and the people, Gen Apirat said.
"I asked everyone [at the discussion] and they told me they have studied Thai history," Gen Apirat said.
He added that the teens said they were aware that the monarchy has played a key role in building the Thai nation.
Although no particular case was mentioned, the discussion came after a recent scandal in which Future Forward Party spokeswoman and MP Pannika Wanich was criticised for a 2010 photo which shows her looking at a photo of King Rama IX while a classmate points at him inappropriately. Ms Pannika has apologised for the photo.