Yes, but not a lot. You can get a rough idea how much a power a switch-mode power supply like this draws by plugging it in with no load connected and see how warm it gets. In general, the hotter it is, the more energy the power supply is consuming. According to Apple's website, a Macbook MB061 consumes 14.1 watts with the screen active, but computer idle; with no load on the transformer it consumes 0.21 watts.