Welcome to Android Central! Interestingly, this GSMArena review does say that the Active is MHL compatible:
Samsung Galaxy S6 Active review: The triathlete - page 3 - GSMArena.com But other articles say that the entire S6 line isn't compatible:
http://blog.clove.co.uk/2014/02/05/m...g-galaxy-need/
This comparison specifically notes that the S6 Active doesn't have MHL while the S5 Active does:
http://www.phonearena.com/phones/com...ones/9310,8665.
I'll keep looking to see if I can find any other info.
Another article saying it does have MHL:
http://allsmartphonesworld.blogspot....ve-review.html.
Obviously, none of this is conclusive, since none of the sources are Samsung themselves. Hopefully someone here can tell us their direct experience!