Most of the sugar comes in breakfast cereals, yoghurts and biscuits.
Adults are consuming double the recommended amount of sugar, the organisation added.
The FSA welcomed new guidelines published by Public Health England, which promised to remove around 200,000 tonnes of sugar from UK diets, per year by 2020.
FSA chairman Heather Hancock said: "The FSA is also working with local cafes and restaurants to encourage displays of calories on menus so that people have the information they need to make healthy choices when eating out.
"The FSA's aim is to have healthier choices widely available and easy for consumers to make wherever they eat."
The Public Health England guidance sets out the recommended sugar limits for nine food groups including biscuits, breakfast cereals and yoghurt, and how reductions could be achieved by the food industry.
In Northern Ireland, the FSA has been working with small and medium-sized businesses on reducing sugar content.
Ms Hancock added: "We know that adults and children in Northern Ireland are eating too much sugar and that most of it comes from everyday foods such as breakfast cereals and yoghurts as well as from foods such as confectionery and biscuits.
"That is why the Food Standards Agency's work with the Northern Ireland food industry is vital in reducing the levels of sugar, saturated fat and salt in the food they manufacture, serve or sell, as well as reducing portion sizes in general."
She said healthy choices should be easy to make.
"Eating a healthy, balanced diet is a key factor in having good health and achieving and maintaining a healthy weight.
"We are committed to collaborating across government and industry in tackling obesity and providing consumers with the opportunities to support and access a healthier lifestyle."