As mentioned, this can be a problem with the binoculars themselves.
If it happens on all binoculars, then it might be your vision, or as Alex mentioned, your viewing technique.
When getting a standard vision test done, convergence isn't always tested, it is easy to test for though, and any optometrist can tell you within a few seconds if you have an issue.
http://www.mayoclinic.com/health/con...-and-diagnosis
http://nacd.org/journal/article11.php