When is the value of average propensity to save negative?

When consumption is more than the income

The average propensity to save equals to the ratio of total saving to total income. Value of average propensity to save will be negative when savings are negative i.e. we  have dis-savings. Dis-savings are done when there is no income and all the basic expenses (autonomous consumption) are done with the help of past savings i.e. consumption is more than the income.