If, by “mediocre”, you mean B- or better, then you probably would want to include the GPA on the resume. Lawyers make money by imagining and anticipating the worst case scenario. That’s what they do. Lawyers are hired by clients to mitigate unforeseen risks, and could be sued for malpractice if they miss any important issues. This has trained us to expect the absolute worst in anything and everything. Lawyers never look at the potential upside. . . .
Because of that, if they don’t see a GPA on a resume, most lawyers would automatically assume that you are hiding something and therefore your GPA must be horrendous. Like C+ or worse. Brace yourself for that. That might be enough to get your resume tossed. They would reason that no rational person would hide their GPA if it was half-way decent . . . and they would be absolutely right. Has anyone ever deleted a 3.5 GPA from his/her resume? Nope.
Of course, if your GPA is C+ or worse, you probably would do no worse if you deleted the GPA from your resume. In that range of grades, it really doesn’t matter whether you have a D+ average versus a C+ average. One caveat might be those law schools that still have a C+ grading curve, in which case you would want the firm to know that you have average grades for your school . . . . but only if the firm you are applying to knows about the horrendous curve. That’s never a sure thing.
On the other hand, if you go to a better school with a generous grading curve (i.e., some elite schools have a B+ or B curve), your “mediocre” grade would be more than sufficient in conjunction with the name of that school. Being average at an elite school is pretty darn good, and that’s good enough even for the vast majority of top firms. Somehow, law firm recruiting offices seem to know all the grading curves of top law schools in the nation. At the top (or better) schools, be sure to put down your “average” grade on your resume, so firms don’t assume you did (way) worse than the average.
Thanks for your question!