The standard state of a gas (at a given temperature) is the state in which fugacity is equal to

The standard state of an gas is taken as ideal gas state where the fugacity is equal to pressure and the pressure is usually taken as $$1,$$ similarly the activity under ideal state is equal to $$1$$ since the activity is the ratio of fugacity at conditions of our interest to the fugacity at standard state and we are taking the standard state as pressure $$= 1$$
So, activity = fugacity = 1.