Beer is acidic. Due to fermentation, which transforms sugars into alcohol and carbon dioxide, beer becomes more acidic.
Typically, popular domestic beers have a pH of 4.0 to 5.0, putting that at the middle line of acidity. Sour beers are slightly more acidic (no surprise) and have a pH between 3.2-3.5, though some lambics can have significantly less acid.
Keep in mind that many non-alcoholic beer brands will remove the alcohol after the beer has been brewed, meaning that those acids are retained. Furthermore, non-alcoholic beers also have additives that increase the acidity level.