Plugin error: wp_enqueue_style was called in incorrectly.

When I activate the plugin, I get the following error:

Notice: wp_enqueue_style was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or login_enqueue_scripts hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.0.) in domain.com/wp-includes/functions.php on line 4204

When I deactivate the plugin, this message goes away.