Yes, for two months, up to a cap
The ElevenLabs pricing page says unused credits roll over for up to two months, up to 2x your monthly quota, so a balance can reach at most 3x the monthly quota. Credits older than that are gone. Rollover does not apply to the $0 entry plan.
In practice this means a quiet month is only banked for two more. A team that saves credits for a quarterly batch job will lose part of them, so size the plan to your steady monthly use, not to your peak.