Using the mouse is a good choice to generate entropy, but there are better methods for generating good random numbers.
For generating a single bitcoin address for personal use, the random generator is likely good enough, but is much much much weaker than a properly random key.
If this is for any kind of system that will be generating many addresses (and therefore be a reasonably attractive target for baddies) it is very much not secure enough.
For any given OS/hardware/programming language combination, quite a bit can be deduced about the state of the random generator, especially if people can make multiple addresses, so that they can gather data. From there its a hop skip and a jump to be predicting other peoples addresses/keys. This becomes an even much worse problem if this is deployed as any kind of shared service in the cloud where the same instance of a generator may be making keys for many users
Use of a real crypographic psudeorandom generator is like 2-3 extra lines of code, and very worth the effort.