Yes, you can. The autofocus on the first field is usually useful. However, there are situations when it gets in the way of a clean user experience. For example, if there is more textual content at the beginning of your form (an HTML block containing information or instructions). In such cases, you really don’t want the cursor to jump on the first input field automatically since the information above would go unseen.
By default, autofocus is enabled. You can disable it easily. Go to the Advanced → Form tab and uncheck the box Autofocus on the first input field of the form.