For estimation of surface wave group velocity at a given period (T), the epicentral distance is divided by the difference in the arrival time of the corresponding group and the origin time of the earthquake. Hence, it is assumed that such waves are generated at the source/epicenter of the earthquake. However, this assumption is not correct. This work describes an effort to understand and quantify the amount of error that can creep into the estimated surface-wave group velocity values due to wrong assumptions used during their estimation. The error may affect the group velocity values especially when regional earthquake data is used for velocity estimation. The analysis was carried out using a horizontal layer over the halfspace model. Errors were estimated at different epicentral distances and periods for different layer thicknesses (H). Also, focal depth (h) was varied from 5 km to just 5 km above the layer boundary for each model. It is observed that for any combination of h, H, and T, error in estimated group velocity decrease rapidly with epicentral distance. The present work gives us some idea about what is the minimum epicentral distance from which data can be included for estimation of group velocity without adding significant error with such a wrong assumption. It is observed that the minimum epicentral distance at which error becomes less than or equal to a given percentage error decreases with increasing focal depth, i.e. lower is the difference between crustal thickness and focal depth, the lower is the error at a given epicentral distance and period. This means that when the difference between crustal thickness and the focal depth is low, even local earthquake data may be used without adding much error in the estimated group velocity values. For a given value of crustal thickness, focal depth, and epicentral distance, error increase with increasing period.