Little red light?

I havve an occasional red light that 'blips' on the bottom of my computer screen. It appears on a random schedule and is very quick (1/10 sec.). Being fairly computer illiterate I will call this the "START" line at the bottom. It shows at the end of the web site indicators to the right and always @1/4 in. from the last noted web site indicator. Does anyone know what it is and/or why it appears?