1. Identify the molecular structure of $\mathrm{CH_4}$

   Methane, $\mathrm{CH_4}$, is a non-linear polyatomic molecule (tetrahedral structure).

2. Translational degrees of freedom

   Any molecule as a whole can move independently along the three mutually perpendicular axes: $x$, $y$, and $z$.

   Therefore, $f_t = 3$

3. Rotational degrees of freedom

   • A linear molecule has $2$ rotational degrees of freedom.
   • A non-linear molecule has $3$ rotational degrees of freedom.

   Since $\mathrm{CH_4}$ is non-linear, it can rotate about all three axes.

   Therefore, $f_r = 3$

4. Match with the options

   We obtained: $f_t = 3, \quad f_r = 3$

   This matches Option B.

5. Final answer

   $\boxed{f_t = 3, \; f_r = 3}$

So, the correct option is B.