With Advanced Ads you can define whether an ad can be displayed on all devices, mobile only or desktop only.
You don’t have to make any changes in order to display an ad on mobile AND desktop devices.
To display an ad on mobile OR desktop devices only, search for the Visitor conditions metabox and add the device condition.
Once you set up the condition you can choose whether to display the ad on mobile and tablets or on desktop.
To display the ad on mobile devices, the setting should look like this:
To hide the ad on mobile devices (resp. display it on desktop devices), the setting should look like this:
Save the ad settings.
Display by browser width
You can set specific device widths for which to display an ad with the help of the Responsive add-on.
Tablets and Mobile
By default, tablets are included in the Mobile condition. In order to exclude or target them specifically, there is a Tablet visitor condition available in the Responsive add-on.
This setting does not work properly on cached websites if you don’t use the cache-busting feature in Advanced Ads Pro.
What else you need to know
Tablet devices will normally be identified as mobile devices.
This option uses the wp_is_mobile() function included in WordPress (Codex). If you are unsatisfied with its functionality, have a look at the function in the WordPress core.