<?php
$isFan = false;

$graphArguments = array(
    'access_token'  => USER's ACCESS TOKEN,
);

// get likes from user
$graphUrl = 'https://graph.facebook.com/me/likes?';
$graphUrl .= http_build_query($graphArguments);

$likes = file_get_contents($graphUrl);
$likes = json_decode($likes);

if($likes && $likes->data) {
    foreach($likes->data as $like) {
        // if user liked our page
        if($like->id == Yii::app()->params['facebookPage']['id']) {
            $isFan = true;
            break;
        }
    }
}

if($isFan) {
    echo 'User is fan!';
} else {
    echo 'User is not a fan!';
}
?>