“Open System Preferences and choose Network In the left-hand pane, highlight Airport if necessary, then click the Advanced button in the lower-right corner.

On the Airport tab, click the button with the – sign to remove all of your known networks, except for your home network.

This should clear up the issue. If it doesn’t, we’ll try something else!”

Planb77 suggests this “Have you tried changing the order of your preferred networks? To do this, head to System Preferences – > Network. Go ahead and unlock the pane if necessary by clicking the small lock icon in the lower left hand corner and entering in your administrator account credentials. Then click the Advanced button. Under the Airport tab you should see a list of all the wi-fi networks your Mac has connected to and remembers. Go ahead and drag your home network to the top of the list to have it automatically connected to first.

And if you so desire, go ahead and remove the random network or networks you wish to remove from the list by clicking the small - button with it highlighted.”