Will it cost you your job?

Interviewers may remain completely quiet after you answer a question. This may be done to see how you handle stress:
    Do you remain calm?
         Are you intimidated? 
                Do you just talk to fill in the silence and risk saying something incoherent?

Scarfile recommends sincerely asking, "Is there anything else I can add to fill in on that point?"  This is an excellent question as the silence is now out of your hands. The responsibility is shot back to the interviewer.  Furthermore, if the interviewer is looking for something additional, you will learn what the interviewer is looking for.

On the other hand, you, yourself, may want to create silence.  You can pause after a difficult question to collect your thoughts.  The interviewer will know you are organizing your train of thought rather than blurting out whatever comes to your head.  You will appear sincere and organized.  Part of eloquence and compelling articulation is knowing when to pause,  whether for emphasis or for organizational purposes,

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The following is another interesting take on silence:  "When I interview people, and they give me an immediate answer, they're often not thinking. So I'm silent. I wait. Because they think they have to keep answering. And it's the second train of thought that's the better answer."-- Robin Leach