The home secretary is banning Muslims Against Crusades (MAC), a group that planned an anti-Armistice Day protest.
It had wanted to repeat a demonstration held last year, when it burned poppies near London's Albert Hall.
Theresa May's order will make membership or support of MAC a criminal offence. It is closely linked to seven other previously-banned groups.
The organisation, now dissolved, said "the call for Islam will never be silenced by any ban or proscription".