Yes, anxiety is a side effect seen with this medication at times.
Here is a break down for you:
The following side effects occur while taking losartan:
More common
Abdominal or stomach pain
anxiety
bladder pain
bloody or cloudy urine
blurred vision
chills
cold sweats
coma
confusion
cool, pale skin
depression
difficult breathing
difficult, burning, or painful urination
dizziness
fast heartbeat
frequent urge to urinate
headache
increased hunger
irregular heartbeat
lower back or side pain
nausea or vomiting
nightmares
numbness or tingling in the hands, feet, or lips
pale skin
seizures
shakiness
shortness of breath
slurred speech
troubled breathing with exertion
unusual bleeding or bruising
unusual tiredness or weakness
weakness or heaviness of the legs
Rare
Arm, back, or jaw pain
chest pain or discomfort
chest tightness or heaviness
dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
fainting
fast, irregular, pounding, or racing heartbeat or pulse
inability to speak
pain or discomfort in the arms, jaw, back, or neck
severe or sudden headache
sweating
swelling or puffiness of the face
temporary blindness
unsteadiness or awkwardness
weakness in the arm or leg on one side of the body, sudden and severe
weakness in the arms, hands, legs, or feet
Incidence not known
Black, tarry stools
bleeding gums
cough
dark urine
difficulty with swallowing
general tiredness and weakness
hives
itching
large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs
light-colored stools
muscle cramps or spasms
muscle pain or stiffness
pinpoint red spots on the skin
puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
skin rash
upper right abdominal or stomach pain
yellow eyes and skin
http://www.drugs.com/sfx/losartan-side-effects.html
How long have you been taking it, and what is your dosage? If you're not new to the Losartan, then I would be willing to bet that any feelings of anxiety you're experiencing isn't related. If the anxiety was related to the medication, it would more likely present itself early on in treatment.
Definitely let your doctor know how you're feeling.
Doesn't look like it has that side effect from the googling I did. Call your pharmacist for a definitive answer though because we can't diagnose you from here.
SIDE EFFECTS: In clinical studies the overall incidence of side effects was similar to placebo. Side effects reported included diarrhea, muscle cramps, dizziness, insomnia, and nasal congestion. Losartan also may cause a persistent cough, increase serum potassium, impotence, and angioedema. Losartan may reduce kidney function in some patients and should not be used by patients who have bilateral renal artery stenosis (narrowing of both arteries going to the kidneys). Rare cases of rhabdomyolysis (muscle breakdown) have been reported.