Global Mobile Communications (GSMs) systems have been developed very rapidly over the past decades. Mobile phone base stations are located almost everywhere nowadays. However, there is a deep concern about the health associated risks of electromagnetic radiation of GSM signals. Unwanted interference between GSM systems and electronic devices is another important issue to be considered. Transforming building surfaces to frequency selective filters is an efficient solution approach to decrease RF exposure levels inside the buildings and to prevent unwanted interference. As a solution approach, single-layer frequency selective surface (FSS) geometry is proposed in this work, which reflects 900 MHz, 1800 MHz and 2100 MHz GSM frequency bands. 1800 MHz and 2100 MHz GSM bands are considered as a single frequency band in this work since they are very close to each other. Ansoft HFSS software is used for simulation, design, and optimization purposes. The equivalent circuit model is also utilized at the design and optimization stages. Achieved results show that proposed FSS element geometry has a stable frequency response up to 60 degrees of incidence angle with minimum of 10 dB attenuation.