Detecting pop-out targets is often considered as a fast, spontaneous and preattentive process. In most experimental studies, however, the observer's attention is explicitly focused on the detection task. We investigated pop-out detection under varying attention conditions: when pop-out displays were (a) not attended and not relevant, (b) attended and relevant and (c) could be attended but were not relevant. Event-related potentials were recorded for color and orientation pop-out targets and target-absent trials. When stimuli were attended, the N2pc component for color pop-outs was more pronounced than N2pc for orientation pop-outs, indicating that saliency modulated the attracting of an observer's attention. Results, however, showed no evidence for preattentive processing of pop-outs when they were not attended and not task relevant.