Yes, you can log in and access to your cTrader account from several different computers at the same time.
You can even trade at the same time.
You just need to make sure that
- You are using the correct login credentials
- The connection is not blocked by any firewalls or ISPs
When you participate a bonus promotion, the rule regarding to the use of multiple devices should be specified in the terms & conditions.
This is to avoid a person using fake IDs to receive bonuses.
You can always choose to trade on multiple cTrader by opening additional accounts too.