If your acne is severe and consists of inflamed bumps that are likely to break open if touched or rubbed, these should be considered as contraindicated for massage techniques such as Swedish or deep tissue. These techniques could easily break open the acne bumps and spread the bacteria laden material. This could be dangerous to both you and your massage therapist.
If your acne is mild, consisting of small red bumps (the kind that will not break open upon touch) then you may consider massage. This would be on a case by case basis, depending on an assessment by your massage therapist.
Always tell your massage therapist during intake, before getting a massage, if you have acne on your back. Discuss the options. Perhaps an acupressure technique, which is performed with clothes and does not use any lubricant, would be better.
Also inform your massage therapist if you are taking any medication, either prescription or over-the-counter, for the condition as massage can influence the effectiveness of the drugs.