Provided is an acrylic flame retardant adhesive composition, including: (A) 100 parts by mass of an acrylic polymer containing a carboxyl group, with a glass transition temperature of 5 to 30° C., (B) 1 to 20 parts by mass of a resol-type phenol resin, (C) 1 to 20 parts by mass of an epoxy resin, (D) 0.1 to 5 parts by mass of a curing accelerator, (E) a bromine-based flame retardant, in sufficient quantity to produce a bromine content within the entire composition, excluding the component (F), of 15 to 40% by mass, and (F) 10 to 100 parts by mass of an inorganic filler. Also provided are an acrylic adhesive sheet that contains an adhesive layer including this composition and a method of bonding two substrates using this acrylic adhesive sheet. The acrylic adhesive sheet exhibits excellent adhesiveness, heat resistance, workability, handling properties and flame retardancy, and the acrylic adhesive composition is useful in the production of such an adhesive sheet.