if the p-v graph is anti clockwise then is the work done by the gas negative?Is it always true?

If you are talking about a circle then you will have to divide it in two parts and take work +ve and -ve according to increase and decrease in volume

 Easiest way is to divide it in upper and lower semi circles, the upper half circle volume decreases in anti clockwise hence work is negative and the lower half part volume increases hence work is positive. This will make the calculation of the area that is work easier which will come out to be equal to area of the circle and will be negative in anti clockwise and positive in clockwise.

I think you have got your answer.