Index: src/bp-templates/bp-nouveau/includes/messages/functions.php
===================================================================
--- src/bp-templates/bp-nouveau/includes/messages/functions.php
+++ src/bp-templates/bp-nouveau/includes/messages/functions.php
@@ -46,19 +46,28 @@
 		return $scripts;
 	}
 
-	return array_merge( $scripts, array(
-		'bp-nouveau-messages-at' => array(
+	$new_scripts  = array();
+	$message_deps = array( 'bp-nouveau', 'json2', 'wp-backbone' );
+
+	// Add mentions if activity component is enabled.
+	if ( bp_is_active( 'activity' ) ) {
+		$new_scripts['bp-nouveau-messages-at'] = array(
 			'file'         => buddypress()->plugin_url . 'bp-activity/js/mentions%s.js',
 			'dependencies' => array( 'bp-nouveau', 'jquery', 'jquery-atwho' ),
 			'version'      => bp_get_version(),
 			'footer'       => true,
-		),
-		'bp-nouveau-messages' => array(
-			'file'         => 'js/buddypress-messages%s.js',
-			'dependencies' => array( 'bp-nouveau', 'json2', 'wp-backbone', 'bp-nouveau-messages-at' ),
-			'footer'       => true,
-		),
-	) );
+		);
+
+		array_push( $message_deps, 'bp-nouveau-messages-at' );
+	}
+
+	$new_scripts['bp-nouveau-messages'] = array(
+		'file'         => 'js/buddypress-messages%s.js',
+		'dependencies' => $message_deps,
+		'footer'       => true,
+	);
+
+	return array_merge( $scripts, $new_scripts );
 }
 
 /**
Index: src/bp-templates/bp-nouveau/js/buddypress-messages.js
===================================================================
--- src/bp-templates/bp-nouveau/js/buddypress-messages.js
+++ src/bp-templates/bp-nouveau/js/buddypress-messages.js
@@ -105,6 +105,11 @@
 			if ( typeof window.tinyMCE === 'undefined' || window.tinyMCE.activeEditor === null || typeof window.tinyMCE.activeEditor === 'undefined' ) {
 				return;
 			} else {
+				// Mentions isn't available, so bail.
+				if ( _.isEmpty( exports.mentions ) ) {
+					return;
+				}
+
 				$( window.tinyMCE.activeEditor.contentDocument.activeElement )
 					.atwho( 'setIframe', $( '#message_content_ifr' )[0] )
 					.bp_mentions( {