It commemorates the moment the guns fell silent at the end of the first world war on the 11 November 1918.
Silence fell at 11:00 GMT to remember servicemen and women killed in battle.
Wreath-laying events have been taking place at war memorials across Northern Ireland.
Belfast Lord Mayor Brian Kingston said it was good to see a large turnout for the ceremony at city hall.
"I was very impressed by the number of people who came along for the Armistice Day two minutes silence at 11am," he said.
"There must have been around 1,000 people here in the Garden of Remembrance beside city hall.
"We see that people, very much, do want to show their appreciation and their understanding for those who served for freedom and democracy that we enjoy today."
Another ceremony was held at the Diamond in Londonderry.
Among those attending was Economy Minister Simon Hamilton.
"I think you're seeing in Northern Ireland increasing numbers of people coming out on the 11th of November and on Remembrance Sunday to pay their respects to those who laid down their lives in the past," he said.
"I think it's one of the great signs of progress that we've made in the last number of years that people are now, on all sides of the community, recognising the sacrifice that both Catholics and Protestants made during the Great War and in other conflicts as well."
Justice Minister Claire Sugden attended a ceremony at Hydebank Wood to remember 32 serving prison officers murdered in Northern Ireland.
"I consider it to be a privilege to be able to attend today's service and meet some of the widows and close relatives of prison service staff who lost their lives in the line of duty," she said.
A two-minute silence has been observed across Northern Ireland and Britain for Armistice Day.