If what you mean by "relaxing" is, physiologically, a lowering of your blood pressure and a reduction of your heart rate, and psychologically, a reduction of stress and worries, then bass fishing is not relaxing for me. I think the physical part is evident, but I should explain the mental part. There are good types of stress and bad types. Bad types would be: personal finances, relationships, work-related worries, etc. I think good types of stress are: worrying about catching a big fish, worrying about a bass coming unbuttoned, worrying about casting accuracy, etc.
So no, bass fishing is not relaxing because I'm sure most people's heart rates go up along with their blood pressure, and most of the time bass fishing is stressful (although it's the good kind of stress).
If what you mean by "relaxing" is getting away from it all and enjoying yourself, then bass fishing is absolutely relaxing.