The comments came as King Maha Vajiralongkorn, 69, was reportedly in Germany on his first documented trip abroad since pro-democracy protests last year morphed into once-unthinkable open criticism of the monarchy, including questioning his prolonged absences from Thailand.
Prime Minister Prayuth Chan-ocha expressed concern some Thais are now "afraid" to stand for the royal anthem, the latest sign of change in a kingdom where the monarch is constitutionally enshrined to be held in "revered worship".
"I'm concerned for those who want to stand, but are afraid to because they don't want to get bullied. It takes bravery to stand up," Prayuth said in a speech at the National Defense College.
In cinemas across the country, moviegoers have for decades stood as the royal anthem played, accompanied by a video of the monarch's achievements, just before movies started.
But lately, many have been observed remaining seated.
On Wednesday, the Thai government also defended laws that punish defaming the monarchy with up to 15 years in prison, as United Nations member states expressed concern over human rights.
Since protests began last year, at least 156 people have been charged under the royal insult law, the Thai Lawyers for Human Rights group says.
Among the protesters' complaints were new powers King Vajiralongkorn has amassed - including direct control of the vast crown fortune and command of two army units - as well as prolonged time abroad since taking the throne in 2016 after his widely-revered father died.
This week, King Vajiralongkorn and his entourage were seen at an airport hotel outside Munich, German tabloid Bild reported on Wednesday.
It was unclear how long he would stay in Germany.
The king traditionally presides over an elaborate Buddhist ceremony in Bangkok that is scheduled for later in November.
The Royal Palace could not be reached for comment on Thursday and has never answered questions about the king's time abroad. It has repeatedly declined to comment on the protests.