A possible cause is having the Wakeup on LAN (WOL) function enabled. To avoid this, the WOL function should be disabled.
How to disable Wakeup on LAN?
Restart the unit and load into the BIOS (depending on the model, hold down either ESC-key or F2-key while powering up).
Use the arrow keys to scroll to the Wake-up on LAN option and change to Disabled using the space bar.
Save changes and exit. (Model specific - END key on some models, and F10 key on others) select Y for Yes.