I founded this solution from http://robinhenniges.com/en/android6-get-mac-address-programmatically and it's working for me! Hope helps!
public static String getMacAddr() {
try {
List<NetworkInterface> all = Collections.list(NetworkInterface.getNetworkInterfaces());
for (NetworkInterface nif : all) {
if (!nif.getName().equalsIgnoreCase("wlan0")) continue;
byte[] macBytes = nif.getHardwareAddress();
if (macBytes == null) {
return "";
}
StringBuilder res1 = new StringBuilder();
for (byte b : macBytes) {
String hex = Integer.toHexString(b & 0xFF);
if (hex.length() == 1)
hex = "0".concat(hex);
res1.append(hex.concat(":"));
}
if (res1.length() > 0) {
res1.deleteCharAt(res1.length() - 1);
}
return res1.toString();
}
} catch (Exception ex) {
}
return "";
}