Be angry? At times, yes! However, we must not sin in our anger and are called to deal with it in a timely manner. Anger is like pain in that it alerts us that something is wrong and motivates us to act. However, anger is also dangerous and often wrongly directed and out of proportion. When you are angry ask: What object of my love is being harmed? Does this anger align with God's love? Is this anger proportionate to the harm being done?
If your anger is a selfish anger, then repent! If it is a godly anger, then respond with restraint and choose to resolve the issue with love and wisdom. Anger is a great short term motivator, but love must govern all we do. Forgive quickly in order to avoid bitterness or rage and be willing to reconcile should a person genuinely repent. At times it is right to be angry! Even when anger is right, however, we must beware of our precarious situation and respond wisely and quickly.