Fed. R. Evid. 606 — Juror’s Competency as a Witness

(a) At the Trial. A juror may not testify as a witness before the other jurors at the trial. If a juror is called to testify, the court must give a party an opportunity to object outside the jury’s presence. (b) During an Inquiry into the Validity of a Verdict or Indictment. (1) Prohibited Testimony or Other Evidence. During an inquiry into the validity of a verdict or indictment, a juror may not testify about any statement made or incident that occurred during the jury’s deliberations; the effect of anything on that juror’s or another juror’s vote; or any juror’s mental processes concerning the verdict or indictment. The court may not receive a juror’s affidavit or evidence of a juror’s statement on these matters. (2) Exceptions. A juror may testify about whether: (A) extraneous prejudicial information was improperly brought to the jury’s attention; (B) an outside influence was improperly brought to bear on any juror; or (C) a mistake was made in entering the verdict on the verdict form.