Im testing antioxidant activity of herbal extracts. I calcu

I’m testing antioxidant activity of herbal extracts. I calculated absorbance- then used Inhib. Acti.%=(A0-A1)/A0x100 to get Inhib. Activity of the extract. A0=ab. of control A1= ab. of extract sample but 4 some im getting neg.,what does this mean? Because I thought that the trend should be positive percentages not negative. I”m not sure if this makes sense, or how I should word my results