Reverse charge mechanism in service tax

Yes. Refer Notification 30/2012.

Is it required even if the service provider has charged service tax in his bill?

Serivce provider is to charge tax as mentioned in the Notification and the balance needs to be paid by the service receiver

Whether the service provider has charged 100% of service tax in his bills or not, your liability as service receiver is fixed to the extent of % mentioned in the notification.  Hence you need to discharge your liability under RCM.