Mac starts up automatically

Solution 1:

You may have your Mac setup to start automatically. To check follow these steps:

1. From the Apple menu, choose System Preferences
2. Select Energy Saver
3. Click on the Schedule button
4. Check the options to see if this is what's causing your problem
5. Make any changes you need to
6. Click OK

Hope this helps!

Solution 2:

Check console.app, it logs how the system was started and why. If it's a Maintenance Wake / Dark Wake going wrong, it behaves like you describe in some cases. If it's a preset, it will say something about an RTC Alarm. If it was an external device, it will also mark it so. Long story short: check the logs.

Solution 3:

Alternatively, do you have it set to respond to Ethernet wake packets and have something wired that might be sending them?