Stephen Vikash Chand, 25, is alleged to have plotted to decapitate Canadian Prime Minister Stephen Harper, according to Mr Chand's lawyer.
"There's an allegation apparently that my client personally indicated that he wanted to behead the prime minister of Canada," said defence lawyer Gary Batasar.
An eight page synopsis of the charges against the group said they planned to storm the Canadian parliament and take hostages to demand that Muslim prisoners be freed and that Canada withdraw troops from Afghanistan, Mr Batasar said.
If the demands were not met they would behead the hostages including the prime minister, he added.
There was also an alleged plan to storm offices of Canadian Broadcasting Corporation (CBC), to press their demands, the lawyer said.
Mr Batasar said Mr Chand had not discussed any of the charges, but added "There's no basis for the allegations as far as I can see."
Ten adult men and five minors appeared in a small, packed courtroom in the Toronto suburb of Brampton.
Allegations shock country
The allegations which are described as an Al-Qaeda-inspired plot to attack high-profile targets in Ontario, Canada's largest province, have rocked the country, and officials have signalled more arrests are coming.
While Justice Maurice Hudson set bail hearings for June 12, heavily-armed police kept watch on a large crowd outside that included dozens of young men and women, some reading the Koran, who said they were friends of the suspects.
Six of the adults have been charged with attempting to set off an explosion to kill people and cause serious damage. The charges against five minors cannot be disclosed under Canadian law.
Authorities said more arrests were expected, possibly this week, as police pursue leads about a group that they say was inspired by the violent ideology of the al Qaeda terrorist network.
Responding to the arrests, the US Border Patrol stepped up inspections of traffic from Canada and put agents on high alert along the 6,400 km border.