No, it is not necessarily zero
Given :
\(∑_i\vec{F_i}\) ≠ 0
Sum of torque about a certain point A,
\(∑_i\vec{r_i}\times\vec{F_i}\) = 0
Sum of torques about any other point B,
\(∑_i(\vec{r_i-a})\times \vec{F_i}=∑^n_{i=1}\vec{r_i}\times \vec{F_i}-a∑_{i=1}\vec{F_i}\)
So, as a and \(∑^n_{i=1}\vec{F_i}\) are not zero.
∴ torque is not necessarily zero about any other point.