Answer:
Yes
May not be zero
Step-by-step explanation:
a) When a acceleration of a system = 0
F = m*a = 0
Hence,
All resultant external forces are zero
b) A system may consists of multiple masses or objects interacting with one another. Hence, those internal are non zero for the system to remain intact
E.g two boxes riding on one another moving at a constant speed.
Hence, a single object system has zero internal forces; however, a multiple objects system will have non zero internal forces