It is nothing unusual. The content of the selenium in your 2% HNO3 is below your blank calibration standard. That is why the instrument shows the concentrations below zero. Of course you do not report the negative values. What you need to do is to set your detection an quantification limits and report the result as below the quantification limit. 

Hi

Thanks for your response. Your explanation is very good. But, negative intensities were observed for an element before aspirating calibration standards in blank solution.

How we can eliminate these negative intensities and what is reason for these negative intensities in blank.