I think there is. To clarify, I think what you are doing is this:
1) Placing an RSI indicator
2) Placing an SMA on the RSI plot (overlaying it so that it represents an SMA of the RSI value)
Like this:
Where the red line is the SMA of the RSI.
What you would think to do now is open the 'Create alert' window by clicking the little clock icon for alerts in the MW toolbar. But, you won't see the options for your RSI or SMA there. I think this is due to a mistake or miss by MotiveWave. I think they do not allow alerts for subgraphs.
So here is what you need to do:
1) Add an RSI study to the chart, but in the Options tab select Price Graph:
2) Add an SMA indicator and as the input set it to the RSI:
3) Then create an alert based on these two lines: