Yes this is possible in a Custom Workflow Activity using Output Parameters. This blog post is useful.
In your C# code, outside of the Execute() function, define an Output Parameter like this:
[Output("Account Name")]
public OutArgument<string> AccountName { get; set; }
Then in your code (that executes within the Execute() function, set the value of your Output Parameter (in this case AccountName) like this:
AccountName.Set(executionContext, "account name"); Replace the "account name" string as appropriate.
Then in your workflow, every step after the step where you have called your custom step will have access to AccountName.