How to control refresh interval

Hi all,
I’m hosting an intranet website by WordPress 3.6 on Centos 6.4 .
I noticed that when users access to intranet website, after browsing some pages, leave browser opened, their browser will refresh intranet website after 5 seconds. In my intranet website access log, I get entries like this:

192.168.14.185 - - [26/Aug/2014:11:54:49 +0700] "POST /wp-admin/admin-ajax.php HTTP/1.1" 200 2
...
192.168.14.185 - - [26/Aug/2014:11:54:54 +0700] "POST /wp-admin/admin-ajax.php HTTP/1.1" 200 2
...
192.168.14.185 - - [26/Aug/2014:11:54:59 +0700] "POST /wp-admin/admin-ajax.php HTTP/1.1" 200 2
...

How can I control it ?