Radio Spectrum sensing has been a topic of strong research in the last years due to its importance to Cognitive Radio (CR) systems. However, in Cognitive Radio Networks (CRNs) with multiple Primary Users (PUs), the Secondary Users (SUs) can often detect PUs that are located outside the sensing range, due to the level of the aggregated interference caused by that PUs. This effect, known as Spatial False Alarm (SFA), degrades the performance of CRNs, because it decreases the SUs' medium access probability. Adopting Energy-based spectrum sensing (EBS) in each SU, this work starts to characterize the interference caused by multiple PUs located outside the sensing area. The interference formulation is then used to derive the probabilities of detection (PD) and false alarm (PFA), and closed form expressions are presented. Several results show that the probabilities PD and PFA are successfully validated through simulation. Finally, the work shows that the SFA can be almost neglected, depending on the path loss factor and on the number of samples collected by the energy detector to decide the spectrum's occupancy state.