Can an overactive bladder be a sign of something more serious?

It definately can be a sign of a more serious problem:

"Causes of Frequent urination:
The following medical conditions are some of the possible causes of Frequent urination. There are likely to be other possible causes, so ask your doctor about your symptoms.

Possible causes of "frequent urination" or related issues include:
Excessive urination - too much urine coming out
Frequent urination attempts - urge to urinate frequently without much urine output.
Urinary dribbling
Urinary urgency
Overflow incontinence (type of Urinary Incontinence) - may cause urinary frequency.
Habitual urination
See also excessive urination
difficulty starting urination (see Urinary symptoms)
weak urination
polyurea
reduced urine

Everyday causes of frequent urination include:
Drinking too much fluid
Caffeine
Alcohol
Normal aging
Urinary tract infections
Upper UTI
Urethral conditions (type of Urinary disorders)
Urethritis - see also causes of urethritis
Urethral infection
Chronic posterior urethral infection
Urethrotrigonitis - in women

Bladder conditions:
Cystitis
Bacterial cystitis (type of Cystitis)
Interstitial cystitis
Bladder stones (type of Urinary stones)
Reduced bladder capacity (see Bladder symptoms) "

http://www.wrongdiagnosis.com/sym/freque...

Some of these causes you might be able to rule out, but you probably should talk to a medical professional about this, especially if it is a recent development.

Are you too thirsty most of the time?
Did you lost your weight?
Check your sugar level in your blood......

u must be black

I had an overactive bladder at one time. I was getting urges to go to the loo when I did need to go. I had such a strong feeling of wanting to go then when I did go nothing happened. My doctor gave me a three week course of tablets and after a week and a half they started to work. Mine wasn't serious. If you have that problem your doctor can prescribe something.