The soft drinks group's latest trading statement disclosed Irn-Bru had performed well in Scotland and had witnessed "excellent" growth in the north of England.
Irn-Bru's performance comes despite no increase in its overall marketing budget over the past 12 months.
But AG Barr, which also owns exotic juice brand Rubicon, warned rising inflation and static household incomes would impact group sales in 2011.
It said sales of Rubicon, which is sold in London corner shops, had grown by 30% and the brand now boasted sales of around £50m.
AG Barr acquired the business in 2008 for £59.8m. It said sales have doubled since the acquisition.
The company has also reported growth across its carbonates range, which includes own-brand flavoured drinks such as cream soda and ginger beer.
The company is anticipating a 5% growth for the three months to 31 January 2011, compared with same period last year.
AG Barr said it had kept its marketing budget at similar levels for the past two years.