Can any one know what this file is about? http://www.symbios.pk/x.dep.PIE.htc? Is it safe to keep on server? I've never seen such before and this is one of highest accesses pages on my site.
At a fast glance, this looks safe and appears to stem from a CSS3 compatibility layer: CSS3 PIE. If you are worried, you can always re-download the file from the website and re-add it, but I would keep a backup first in case of any version incompatibilities.
The file on your web server doesn't match Beta 1.0.0's PIE.htc exactly but it is rather similar and it also already good to know that a .htc file does indeed come from CSS3 PIE. The extension of a file obviously doesn't say much about its contents but it's still reassuring to see that it is an expected file ending. (I've never encountered an .htc file before, so this raised some concerns for me.)
As for it being visited a lot, this doesn't have to mean anything. Possibly the file is being checked out by bots or someone is hotlinking your JS file; it's hard to say without context but if it's a JavaScript file from some framework you should be fine. The good news here is that this is JavaScript, so it can't compromise your server (but it could attack a browser loading the file).
If all else fails and you know where your pages use this file, you could try renaming the file so anyone hotlinking or just guessing for the existence of the file would have a tougher time. I don't really understand why someone would take interest in a small JavaScript file, though.
Interestingly, visiting your main page at symbios.pk doesn't load the file, though. Maybe some back-end module? If multiple people are working on the website, I would suggest asking all of the developers if they know about this file. It would be interesting to compare the creation date with that of similar files.