It is said that in Blackhole 100% part of the mass is getting converted into energy. Then how come Blackhole is having mass ?
I believe when most scientists refer to the mass of a blackhole - i.e. a blackhole having the mass of a billion Suns, what they really mean is that the calculated gravitational pull of the blackhole is equivalent to that of such a mass would it exists at the location of the blackhole.
PS: Perhaps you could also bring some reference with respect to where exactly have you heard that 'It is said that in Blackhole 100% part of the mass is getting converted into energy'
The truth is no one truly knows if 100% of the mass is being converted into energy. So without this assumption many other things are possible. Some think that since there is a constant flow of mass into the black hole, the conversion into energy is not keeping up with the rate the matter is being consumed, therefore the mass would remain substantially large.