
Not no anger. Some Christians think that getting angry is always a sin. But it is a sin when we are not angry when we should be angry about things that anger God.
Not blow anger. Blowing up in anger without self-control (so easy to do!) is always a sin. Thus, Prov 16:32 says that one who controls his temper is greater than one who conquers a city.
But slow to anger, for our God is "the compassionate and gracious God, slow to anger, abounding in love and faithfulness" (Exo 34:6) (Num 14:18, Ps 103:8, etc). Otherwise, God would surely have incinerated us already! The cross of our Lord Jesus Christ is the perfect manifestation of God's slow anger, for God put His Son on the cross instead of us.