Facebook Problem, Help Please. . . . . . .

Please look at the picture and tell me why that happens almost every time I try to comment and it happens no matter what browser I use, not sure if it is a setting or Facebook or my computer, thanks in advance.

AT sign on FB.jpg
I should have updated this a lot sooner but the problem I had is now gone and I don't know why but I am glad it is gone, thanks for the replies and help. . . . .